1 If you are using ikiwiki to render pages that only you can edit, do not
2 generate any wrappers, and do not use the cgi, then there are no more
3 security issues with this program than with cat(1). If, however, you let
4 others edit pages in your wiki, then some possible security issues do need
7 If you find a new security vulnerability, please email the maintainers
8 privately instead of listing it in a public bug tracker, so that we can
9 arrange for coordinated disclosure when a fix is available. The maintainers
10 are [[Joey Hess|joey]] (<joey@kitenet.net>),
11 [[Simon McVittie|smcv]] (<smcv@debian.org>)
12 and [[Amitai Schleier|schmonz]] (<schmonz-web-ikiwiki@schmonz.com>).
20 _(The list of things to fix.)_
24 Anyone with direct commit access can forge "web commit from foo" and
25 make it appear on [[RecentChanges]] like foo committed. One way to avoid
26 this would be to limit web commits to those done by a certain user.
28 ## other stuff to look at
30 I have been meaning to see if any CRLF injection type things can be
39 ## image file etc attacks
41 If it enounters a file type it does not understand, ikiwiki just copies it
42 into place. So if you let users add any kind of file they like, they can
43 upload images, movies, windows executables, css files, etc (though not html
44 files). If these files exploit security holes in the browser of someone
45 who's viewing the wiki, that can be a security problem.
47 Of course nobody else seems to worry about this in other wikis, so should we?
49 People with direct commit access can upload such files
50 (and if you wanted to you could block that with a pre-commit hook).
52 The attachments plugin is not enabled by default. If you choose to
53 enable it, you should make use of its powerful abilities to filter allowed
54 types of attachments, and only let trusted users upload.
56 It is possible to embed an image in a page edited over the web, by using
57 `img src="data:image/png;"`. Ikiwiki's htmlscrubber only allows `data:`
58 urls to be used for `image/*` mime types. It's possible that some broken
59 browser might ignore the mime type and if the data provided is not an
60 image, instead run it as javascript, or something evil like that. Hopefully
61 not many browsers are that broken.
63 ## multiple accessors of wiki directory
65 If multiple people can directly write to the source directory ikiwiki is
66 using, or to the destination directory it writes files to, then one can
67 cause trouble for the other when they run ikiwiki through symlink attacks.
69 So it's best if only one person can ever directly write to those directories.
73 Setup files are not safe to keep in the same revision control repository
74 with the rest of the wiki. Just don't do it.
76 ## page locking can be bypassed via direct commits
78 A locked page can only be edited on the web by an admin, but anyone who is
79 allowed to commit directly to the repository can bypass this. This is by
80 design, although a pre-commit hook could be used to prevent editing of
81 locked pages, if you really need to.
85 If your web server does any parsing of special sorts of files (for example,
86 server parsed html files), then if you let anyone else add files to the wiki,
87 they can try to use this to exploit your web server.
93 _(AKA, the assumptions that will be the root of most security holes...)_
95 ## exploiting ikiwiki with bad content
97 Someone could add bad content to the wiki and hope to exploit ikiwiki.
98 Note that ikiwiki runs with perl taint checks on, so this is unlikely.
100 One fun thing in ikiwiki is its handling of a PageSpec, which involves
101 translating it into perl and running the perl. Of course, this is done
102 *very* carefully to guard against injecting arbitrary perl code.
104 ## publishing cgi scripts
106 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
107 rather, the script is published, but it's not marked executable (except in
108 the case of "destination directory file replacement" below), so hopefully
109 your web server will not run it.
113 `ikiwiki --wrapper` is intended to generate a wrapper program that
114 runs ikiwiki to update a given wiki. The wrapper can in turn be made suid,
115 for example to be used in a [[post-commit]] hook by people who cannot write
116 to the html pages, etc.
118 If the wrapper program is made suid, then any bugs in this wrapper would be
119 security holes. The wrapper is written as securely as I know how, is based
120 on code that has a history of security use long before ikiwiki, and there's
125 ikiwiki does not expose untrusted data to the shell. In fact it doesn't use
126 `system(3)` at all, and the only use of backticks is on data supplied by the
127 wiki admin and untainted filenames.
129 Ikiwiki was developed and used for a long time with perl's taint checking
130 turned on as a second layer of defense against shell and other exploits. Due
131 to a strange [bug](http://bugs.debian.org/411786) in perl, taint checking
132 is currently disabled for production builds of ikiwiki.
136 When ikiwiki runs as a cgi to edit a page, it is passed the name of the
137 page to edit. It has to make sure to sanitise this page, to prevent eg,
138 editing of ../../../foo, or editing of files that are not part of the wiki,
139 such as subversion dotfiles. This is done by sanitising the filename
140 removing unallowed characters, then making sure it doesn't start with "/"
141 or contain ".." or "/.svn/", etc. Annoyingly ad-hoc, this kind of code is
142 where security holes breed. It needs a test suite at the very least.
144 ## CGI::Session security
146 I've audited this module and it is massively insecure by default. ikiwiki
147 uses it in one of the few secure ways; by forcing it to write to a
148 directory it controls (and not /tmp) and by setting a umask that makes the
149 file not be world readable.
151 ## cgi password security
153 Login to the wiki using [[plugins/passwordauth]] involves sending a password
154 in cleartext over the net. Cracking the password only allows editing the wiki
155 as that user though. If you care, you can use https, I suppose. If you do use
156 https either for all of the wiki, or just the cgi access, then consider using
157 the sslcookie option. Using [[plugins/openid]] is a potentially better option.
159 ## XSS holes in CGI output
161 ikiwiki has been audited to ensure that all cgi script input/output
162 is sanitised to prevent XSS attacks. For example, a user can't register
163 with a username containing html code (anymore).
165 It's difficult to know for sure if all such avenues have really been
168 ## HTML::Template security
170 If the [[plugins/template]] plugin is enabled, all users can modify templates
171 like any other part of the wiki. Some trusted users can modify templates
172 without it too. This assumes that HTML::Template is secure
173 when used with untrusted/malicious templates. (Note that includes are not
180 The security of [[plugins]] depends on how well they're written and what
181 external tools they use. The plugins included in ikiwiki are all held to
182 the same standards as the rest of ikiwiki, but with that said, here are
183 some security notes for them.
185 * The [[plugins/img]] plugin assumes that imagemagick/perlmagick are secure
186 from malformed image attacks for at least the formats listed in
187 `img_allowed_formats`. Imagemagick has had security holes in the
188 past. To be able to exploit such a hole, a user would need to be able to
189 upload images to the wiki.
195 _(Unless otherwise noted, these were discovered and immediately fixed by the
196 ikiwiki developers.)_
198 ## destination directory file replacement
200 Any file in the destination directory that is a valid page filename can be
201 replaced, even if it was not originally rendered from a page. For example,
202 ikiwiki.cgi could be edited in the wiki, and it would write out a
203 replacement. File permission is preseved. Yipes!
205 This was fixed by making ikiwiki check if the file it's writing to exists;
206 if it does then it has to be a file that it's aware of creating before, or
207 it will refuse to create it.
209 Still, this sort of attack is something to keep in mind.
213 Could a committer trick ikiwiki into following a symlink and operating on
214 some other tree that it shouldn't? svn supports symlinks, so one can get
215 into the repo. ikiwiki uses File::Find to traverse the repo, and does not
216 tell it to follow symlinks, but it might be possible to race replacing a
217 directory with a symlink and trick it into following the link.
219 Also, if someone checks in a symlink to /etc/passwd, ikiwiki would read and
220 publish that, which could be used to expose files a committer otherwise
223 To avoid this, ikiwiki will skip over symlinks when scanning for pages, and
224 uses locking to prevent more than one instance running at a time. The lock
225 prevents one ikiwiki from running a svn up/git pull/etc at the wrong time
226 to race another ikiwiki. So only attackers who can write to the working
227 copy on their own can race it.
229 ## symlink + cgi attacks
231 Similarly, a commit of a symlink could be made, ikiwiki ignores it
232 because of the above, but the symlink is still there, and then you edit the
233 page from the web, which follows the symlink when reading the page
234 (exposing the content), and again when saving the changed page (changing
237 This was fixed for page saving by making ikiwiki refuse to write to files
238 that are symlinks, or that are in subdirectories that are symlinks,
239 combined with the above locking.
241 For page editing, it's fixed by ikiwiki checking to make sure that it
242 already has found a page by scanning the tree, before loading it for
243 editing, which as described above, also is done in a way that avoids
246 ## underlaydir override attacks
248 ikiwiki also scans an underlaydir for pages, this is used to provide stock
249 pages to all wikis w/o needing to copy them into the wiki. Since ikiwiki
250 internally stores only the base filename from the underlaydir or srcdir,
251 and searches for a file in either directory when reading a page source,
252 there is the potential for ikiwiki's scanner to reject a file from the
253 srcdir for some reason (such as it being contained in a directory that is
254 symlinked in), find a valid copy of the file in the underlaydir, and then
255 when loading the file, mistakenly load the bad file from the srcdir.
257 This attack is avoided by making ikiwiki refuse to add any files from the
258 underlaydir if a file also exists in the srcdir with the same name.
260 ## multiple page source issues
262 Note that I previously worried that underlay override attacks could also be
263 accomplished if ikiwiki were extended to support other page markup
264 languages besides markdown. However, a closer look indicates that this is
265 not a problem: ikiwiki does preserve the file extension when storing the
266 source filename of a page, so a file with another extension that renders to
267 the same page name can't bypass the check. Ie, ikiwiki won't skip foo.rst
268 in the srcdir, find foo.mdwn in the underlay, decide to render page foo and
269 then read the bad foo.mdwn. Instead it will remember the .rst extension and
270 only render a file with that extension.
272 ## XSS attacks in page content
274 ikiwiki supports protecting users from their own broken browsers via the
275 [[plugins/htmlscrubber]] plugin, which is enabled by default.
279 It's was possible to force a whole series of svn commits to appear to
280 have come just before yours, by forging svn log output. This was
281 guarded against by using svn log --xml.
283 ikiwiki escapes any html in svn commit logs to prevent other mischief.
287 XML::Parser is used by the aggregation plugin, and has some security holes.
288 Bug #[378411](http://bugs.debian.org/378411) does not
289 seem to affect our use, since the data is not encoded as utf-8 at that
290 point. #[378412](http://bugs.debian.org/378412) could affect us, although it
291 doesn't seem very exploitable. It has a simple fix, and has been fixed in
296 Various directives that cause one page to be included into another could
297 be exploited to DOS the wiki, by causing a loop. Ikiwiki has always guarded
298 against this one way or another; the current solution should detect all
299 types of loops involving preprocessor directives.
301 ## Online editing of existing css and images
303 A bug in ikiwiki allowed the web-based editor to edit any file that was in
304 the wiki, not just files that are page sources. So an attacker (or a
305 genuinely helpful user, which is how the hole came to light) could edit
306 files like style.css. It is also theoretically possible that an attacker
307 could have used this hole to edit images or other files in the wiki, with
308 some difficulty, since all editing would happen in a textarea.
310 This hole was discovered on 10 Feb 2007 and fixed the same day with the
311 release of ikiwiki 1.42. A fix was also backported to Debian etch, as
312 version 1.33.1. I recommend upgrading to one of these versions if your wiki
315 ## html insertion via title
317 Missing html escaping of the title contents allowed a web-based editor to
318 insert arbitrary html inside the title tag of a page. Since that part of
319 the page is not processed by the htmlscrubber, evil html could be injected.
321 This hole was discovered on 21 March 2007 and fixed the same day (er, hour)
322 with the release of ikiwiki 1.46. A fix was also backported to Debian etch,
323 as version 1.33.2. I recommend upgrading to one of these versions if your
324 wiki allows web editing or aggregates feeds.
326 ## javascript insertion via meta tags
328 It was possible to use the meta plugin's meta tags to insert arbitrary
329 url contents, which could be used to insert stylesheet information
330 containing javascript. This was fixed by sanitising meta tags.
332 This hole was discovered on 21 March 2007 and fixed the same day
333 with the release of ikiwiki 1.47. A fix was also backported to Debian etch,
334 as version 1.33.3. I recommend upgrading to one of these versions if your
335 wiki can be edited by third parties.
337 ## insufficient checking for symlinks in srcdir path
339 Ikiwiki did not check if path to the srcdir to contained a symlink. If an
340 attacker had commit access to the directories in the path, they could
341 change it to a symlink, causing ikiwiki to read and publish files that were
342 not intended to be published. (But not write to them due to other checks.)
344 In most configurations, this is not exploitable, because the srcdir is
345 checked out of revision control, but the directories leading up to it are
346 not. Or, the srcdir is a single subdirectory of a project in revision
347 control (ie, `ikiwiki/doc`), and if the subdirectory were a symlink,
348 ikiwiki would still typically not follow it.
350 There are at least two configurations where this is exploitable:
352 * If the srcdir is a deeper subdirectory of a project. For example if it is
353 `project/foo/doc`, an an attacker can replace `foo` with a symlink to a
354 directory containing a `doc` directory (not a symlink), then ikiwiki
355 would follow the symlink.
356 * If the path to the srcdir in ikiwiki's configuration ended in "/",
357 and the srcdir is a single subdirectory of a project, (ie,
358 `ikiwiki/doc/`), the srcdir could be a symlink and ikiwiki would not
361 This security hole was discovered on 26 November 2007 and fixed the same
362 day with the release of ikiwiki 2.14. I recommend upgrading to this version
363 if your wiki can be committed to by third parties. Alternatively, don't use
364 a trailing slash in the srcdir, and avoid the (unusual) configurations that
365 allow the security hole to be exploited.
367 ## javascript insertion via uris
369 The htmlscrubber did not block javascript in uris. This was fixed by adding
370 a whitelist of valid uri types, which does not include javascript.
371 ([[!debcve CVE-2008-0809]]) Some urls specifyable by the meta plugin could also
372 theoretically have been used to inject javascript; this was also blocked
373 ([[!debcve CVE-2008-0808]]).
375 This hole was discovered on 10 February 2008 and fixed the same day
376 with the release of ikiwiki 2.31.1. (And a few subsequent versions..)
377 A fix was also backported to Debian etch, as version 1.33.4. I recommend
378 upgrading to one of these versions if your wiki can be edited by third
381 ## Cross Site Request Forging
383 Cross Site Request Forging could be used to constuct a link that would
384 change a logged-in user's password or other preferences if they clicked on
385 the link. It could also be used to construct a link that would cause a wiki
386 page to be modified by a logged-in user. ([[!debcve CVE-2008-0165]])
388 These holes were discovered on 10 April 2008 and fixed the same day with
389 the release of ikiwiki 2.42. A fix was also backported to Debian etch, as
390 version 1.33.5. I recommend upgrading to one of these versions.
392 ## Cleartext passwords
394 Until version 2.48, ikiwiki stored passwords in cleartext in the `userdb`.
395 That risks exposing all users' passwords if the file is somehow exposed. To
396 pre-emtively guard against that, current versions of ikiwiki store password
397 hashes (using Eksblowfish).
399 If you use the [[plugins/passwordauth]] plugin, I recommend upgrading to
400 ikiwiki 2.48, installing the [[!cpan Authen::Passphrase]] perl module, and running
401 `ikiwiki-transition hashpassword` to replace all existing cleartext passwords
402 with strong blowfish hashes.
404 You might also consider changing to [[plugins/openid]], which does not
405 require ikiwiki deal with passwords at all, and does not involve users sending
406 passwords in cleartext over the net to log in, either.
408 ## Empty password security hole
410 This hole allowed ikiwiki to accept logins using empty passwords, to openid
411 accounts that didn't use a password. It was introduced in version 1.34, and
412 fixed in version 2.48. The [bug](http://bugs.debian.org/483770) was
413 discovered on 30 May 2008 and fixed the same day. ([[!debcve CVE-2008-0169]])
415 I recommend upgrading to 2.48 immediatly if your wiki allows both password
418 ## Malformed UTF-8 DOS
420 Feeding ikiwiki page sources containing certian forms of malformed UTF-8
421 can cause it to crash. This can potentially be used for a denial of service
424 intrigeri discovered this problem on 12 Nov 2008 and a patch put in place
425 later that day, in version 2.70. The fix was backported to testing as version
426 2.53.3, and to stable as version 1.33.7.
428 ## Insufficient blacklisting in teximg plugin
430 Josh Triplett discovered on 28 Aug 2009 that the teximg plugin's
431 blacklisting of insecure TeX commands was insufficient; it could be
432 bypassed and used to read arbitrary files. This was fixed by
433 enabling TeX configuration options that disallow unsafe TeX commands.
434 The fix was released on 30 Aug 2009 in version 3.1415926, and was
435 backported to stable in version 2.53.4. If you use the teximg plugin,
436 I recommend upgrading. ([[!debcve CVE-2009-2944]])
438 ## javascript insertion via svg uris
440 Ivan Shmakov pointed out that the htmlscrubber allowed `data:image/*` urls,
441 including `data:image/svg+xml`. But svg can contain javascript, so that is
444 This hole was discovered on 12 March 2010 and fixed the same day
445 with the release of ikiwiki 3.20100312.
446 A fix was also backported to Debian etch, as version 2.53.5. I recommend
447 upgrading to one of these versions if your wiki can be edited by third
450 ## javascript insertion via insufficient htmlscrubbing of comments
452 Kevin Riggle noticed that it was not possible to configure
453 `htmlscrubber_skip` to scrub comments while leaving unscubbed the text
454 of eg, blog posts. Confusingly, setting it to "* and !comment(*)" did not
457 Additionally, it was discovered that comments' html was never scrubbed during
458 preview or moderation of comments with such a configuration.
460 These problems were discovered on 12 November 2010 and fixed the same
461 hour with the release of ikiwiki 3.20101112. ([[!debcve CVE-2010-1673]])
463 ## javascript insertion via insufficient checking in comments
465 Dave B noticed that attempting to comment on an illegal page name could be
466 used for an XSS attack.
468 This hole was discovered on 22 Jan 2011 and fixed the same day with
469 the release of ikiwiki 3.20110122. A fix was backported to Debian squeeze,
470 as version 3.20100815.5. An upgrade is recommended for sites
471 with the comments plugin enabled. ([[!debcve CVE-2011-0428]])
473 ## possible javascript insertion via insufficient htmlscrubbing of alternate stylesheets
475 Giuseppe Bilotta noticed that 'meta stylesheet` directives allowed anyone
476 who could upload a malicious stylesheet to a site to add it to a
477 page as an alternate stylesheet, or replacing the default stylesheet.
479 This hole was discovered on 28 Mar 2011 and fixed the same hour with
480 the release of ikiwiki 3.20110328. A fix was backported to Debian squeeze,
481 as version 3.20100815.6. An upgrade is recommended for sites that have
482 untrusted committers, or have the attachments plugin enabled.
483 ([[!debcve CVE-2011-1401]])
485 ## tty hijacking via ikiwiki-mass-rebuild
487 Ludwig Nussel discovered a way for users to hijack root's tty when
488 ikiwiki-mass-rebuild was run. Additionally, there was some potential
489 for information disclosure via symlinks. ([[!debcve CVE-2011-1408]])
491 This hole was discovered on 8 June 2011 and fixed the same day with
492 the release of ikiwiki 3.20110608. Note that the fix is dependant on
493 a version of su that has a similar hole fixed. Version 4.1.5 of the shadow
494 package contains the fixed su; [[!debbug 628843]] tracks fixing the hole in
495 Debian. An upgrade is a must for any sites that have `ikiwiki-update-wikilist`
496 installed suid (not the default), and whose admins run `ikiwiki-mass-rebuild`.
498 ## javascript insertion via meta tags
500 Raúl Benencia discovered an additional XSS exposure in the meta plugin.
501 ([[!debcve CVE-2012-0220]])
503 This hole was discovered on 16 May 2012 and fixed the same day with
504 the release of ikiwiki 3.20120516. A fix was backported to Debian squeeze,
505 as version 3.20100815.9. An upgrade is recommended for all sites.
507 ## XSS via openid selector
509 Raghav Bisht discovered this XSS in the openid selector. ([[!debcve CVE-2015-2793]])
511 The hole was reported on March 24th, a fix was developed on March 27th,
512 and the fixed version 3.20150329 was released on the 29th. A fix was backported
513 to Debian jessie as version 3.20141016.2 and to Debian wheezy as version
514 3.20120629.2. An upgrade is recommended for sites using CGI and openid.
516 ## XSS via error messages
518 CGI error messages did not escape HTML meta-characters, potentially
519 allowing an attacker to carry out cross-site scripting by directing a
520 user to a URL that would result in a crafted ikiwiki error message. This
521 was discovered on 4 May by the ikiwiki developers, and the fixed version
522 3.20160506 was released on 6 May. The same fixes were backported to Debian
523 8 "jessie" in version 3.20141016.3. A backport to Debian 7 "wheezy" is
526 An upgrade is recommended for sites using
527 the CGI. ([[!debcve CVE-2016-4561]], OVE-20160505-0012)
529 ## ImageMagick CVE-2016–3714 ("ImageTragick")
531 ikiwiki 3.20160506 and 3.20141016.3 attempt to mitigate
532 [[!debcve CVE-2016-3714]], and any
533 future ImageMagick vulnerabilities that resemble it, by restricting the
534 image formats that the [[ikiwiki/directive/img]] directive is willing to
535 resize. An upgrade is recommended for sites where an untrusted user is
536 able to attach images. Upgrading ImageMagick to a version where
537 CVE-2016-3714 has been fixed is also recommended, but at the time of
538 writing no such version is available.
540 ## Perl CVE-2016-1238 (current working directory in search path)
542 ikiwiki 3.20160728 attempts to mitigate [[!debcve CVE-2016-1238]] by
543 removing `'.'` from the Perl library search path. An attacker with write
544 access to ikiwiki's current working directory could potentially use this
545 vulnerability to execute arbitrary Perl code. An upgrade is recommended
546 for sites where an untrusted user is able to attach files with arbitrary
547 names and/or run a setuid ikiwiki wrapper with a working directory of
550 ## <span id="cve-2016-9645">Editing restriction bypass for git revert</span>
552 intrigeri discovered that a web or git user could revert a change to a
553 page they are not allowed to edit, if the change being reverted was made
554 before the page was moved from a location where that user had permission
555 to edit it. For example, if a file is moved from `drafts/policy.mdwn`
556 (editable by less-trusted users) to `policy.mdwn` (only editable
557 by more-trusted users), a less-trusted user could revert a change
558 that was made to `drafts/policy.mdwn` prior to that move, and it would
559 result in `policy.mdwn` being altered.
561 This affects sites with the `git` VCS and the `recentchanges` plugin,
562 which are both used in most ikiwiki installations.
564 This bug was reported on 2016-12-17. A partially fixed version
565 3.20161219 was released on 2016-12-19, but the solution used in that
566 version was not effective with git versions older than 2.8.0.
567 A more complete fix was released on 2016-12-29 in version 3.20161229,
568 with fixes backported to Debian 8 in version 3.20141016.4.
570 ([[!debcve CVE-2016-10026]] represents the original vulnerability.
571 [[!debcve CVE-2016-9645]]/OVE-20161226-0002 represents the vulnerability
572 in 3.20161219 caused by the incomplete fix.)
574 ## <span id="cve-2016-9646">Commit metadata forgery via CGI::FormBuilder context-dependent APIs</span>
576 When CGI::FormBuilder->field("foo") is called in list context (and
577 in particular in the arguments to a subroutine that takes named
578 arguments), it can return zero or more values for foo from the CGI
579 request, rather than the expected single value. This breaks the usual
580 Perl parsing convention for named arguments, similar to CVE-2014-1572
581 in Bugzilla (which was caused by a similar API design issue in CGI.pm).
583 In ikiwiki, this appears to have been exploitable in two places, both
584 of them relatively minor:
586 * in the comments plugin, an attacker who was able to post a comment
587 could give it a user-specified author and author-URL even if the wiki
588 configuration did not allow for that, by crafting multiple values
590 * in the editpage plugin, an attacker who was able to edit a page
591 could potentially forge commit authorship (attribute their edit to
592 someone else) by crafting multiple values for the rcsinfo field
594 This was fixed in ikiwiki 3.20161229, with fixes backported to Debian 8
595 in version 3.20141016.4.
597 ([[!debcve CVE-2016-9646]]/OVE-20161226-0001)
599 ## <span id="cve-2017-0356">Authentication bypass via repeated parameters</span>
601 The ikiwiki maintainers discovered further flaws similar to CVE-2016-9646
602 in the passwordauth plugin's use of CGI::FormBuilder, with a more
605 * An attacker who can log in to a site with a password can log in
606 as a different and potentially more privileged user.
607 * An attacker who can create a new account can set arbitrary fields
608 in the user database for that account.
610 This was fixed in ikiwiki 3.20170111, with fixes backported to Debian 8
611 in version 3.20141016.4.
613 ([[!debcve CVE-2017-0356]]/OVE-20170111-0001)
615 ## <span id="cve-2019-9187">Server-side request forgery via aggregate plugin</span>
617 The ikiwiki maintainers discovered that the [[plugins/aggregate]] plugin
618 did not use [[!cpan LWPx::ParanoidAgent]]. On sites where the
619 aggregate plugin is enabled, authorized wiki editors could tell ikiwiki
620 to fetch potentially undesired URIs even if LWPx::ParanoidAgent was
623 * local files via `file:` URIs
624 * other URI schemes that might be misused by attackers, such as `gopher:`
625 * hosts that resolve to loopback IP addresses (127.x.x.x)
626 * hosts that resolve to RFC 1918 IP addresses (192.168.x.x etc.)
628 This could be used by an attacker to publish information that should not have
629 been accessible, cause denial of service by requesting "tarpit" URIs that are
630 slow to respond, or cause undesired side-effects if local web servers implement
631 ["unsafe"](https://tools.ietf.org/html/rfc7231#section-4.2.1) GET requests.
632 ([[!debcve CVE-2019-9187]])
634 Additionally, if the LWPx::ParanoidAgent module was not installed, the
635 [[plugins/blogspam]], [[plugins/openid]] and [[plugins/pinger]] plugins
636 would fall back to [[!cpan LWP]], which is susceptible to similar attacks.
637 This is unlikely to be a practical problem for the blogspam plugin because
638 the URL it requests is under the control of the wiki administrator, but
639 the openid plugin can request URLs controlled by unauthenticated remote
640 users, and the pinger plugin can request URLs controlled by authorized
643 This is addressed in ikiwiki 3.20190228 as follows, with the same fixes
644 backported to Debian 9 in version 3.20170111.1:
646 * URI schemes other than `http:` and `https:` are not accepted, preventing
647 access to `file:`, `gopher:`, etc.
649 * If a proxy is [[configured in the ikiwiki setup file|tips/using_a_proxy]],
650 it is used for all outgoing `http:` and `https:` requests. In this case
651 the proxy is responsible for blocking any requests that are undesired,
652 including loopback or RFC 1918 addresses.
654 * If a proxy is not configured, and LWPx::ParanoidAgent is installed,
655 it will be used. This prevents loopback and RFC 1918 IP addresses, and
656 sets a timeout to avoid denial of service via "tarpit" URIs.
658 * Otherwise, the ordinary LWP user-agent will be used. This allows requests
659 to loopback and RFC 1918 IP addresses, and has less robust timeout
660 behaviour. We are not treating this as a vulnerability: if this
661 behaviour is not acceptable for your site, please make sure to install
662 LWPx::ParanoidAgent or disable the affected plugins.