From 40de619d4968ecd7dc0086ca5118746bc3db3860 Mon Sep 17 00:00:00 2001 From: intrigeri Date: Sat, 17 Jan 2009 13:50:19 +0100 Subject: po(doc): moved security analysis to its own page Signed-off-by: intrigeri --- doc/plugins/po/security.mdwn | 206 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 206 insertions(+) create mode 100644 doc/plugins/po/security.mdwn (limited to 'doc/plugins/po/security.mdwn') diff --git a/doc/plugins/po/security.mdwn b/doc/plugins/po/security.mdwn new file mode 100644 index 000000000..318083669 --- /dev/null +++ b/doc/plugins/po/security.mdwn @@ -0,0 +1,206 @@ +[[!toc levels=2]] + +---- + +# Probable holes + +_(The list of things to fix.)_ + +## po4a-gettextize + +* po4a CVS 2009-01-16 +* Perl 5.10.0 + +`po4a-gettextize` uses more or less the same po4a features as our +`refreshpot` function. + +Without specifying an input charset, zzuf'ed `po4a-gettextize` quickly +errors out, complaining it was not able to detect the input charset; +it leaves no incomplete file on disk. I therefore had to pretend the +input was in UTF-8, as does the po plugin. + + zzuf -c -s 13 -r 0.1 \ + po4a-gettextize -f text -o markdown -M utf-8 -L utf-8 \ + -m GPL-3 -p GPL-3.pot + +Crashes with: + + Malformed UTF-8 character (UTF-16 surrogate 0xdfa4) in substitution + iterator at /usr/share/perl5/Locale/Po4a/Po.pm line 1449. + Malformed UTF-8 character (fatal) at /usr/share/perl5/Locale/Po4a/Po.pm + line 1449. + +An incomplete pot file is left on disk. Unfortunately Po.pm tells us +nothing about the place where the crash happens. + +> It's fairly standard perl behavior when fed malformed utf-8. As long +> as it doesn't crash ikiwiki, it's probably acceptable. Ikiwiki can +> do some similar things itself when fed malformed utf-8 (doesn't +> crash tho) --[[Joey]] + +---- + +# Potential gotchas + +_(Things not to do.)_ + + +## Blindly activating more po4a format modules + +The format modules we want to use have to be checked, as not all are +safe (e.g. the LaTeX module's behaviour is changed by commands +included in the content); they may use regexps generated from +the content. + +---- + +# Hopefully non-holes + +_(AKA, the assumptions that will be the root of most security holes...)_ + +## PO file features + +No [documented](http://www.gnu.org/software/gettext/manual/gettext.html#PO-Files) +directive that can be put in po files is supposed to cause mischief +(ie, include other files, run commands, crash gettext, whatever). + +## gettext + +### Security history + +The only past security issue I could find in GNU gettext is +[CVE-2004-0966](http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2004-0966), +*i.e.* [Debian bug #278283](http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=278283): +the autopoint and gettextize scripts in the GNU gettext package (1.14 +and later versions) may allow local users to overwrite files via +a symlink attack on temporary files. + +This plugin would not have allowed to exploit this bug, as it does not +use, either directly or indirectly, the faulty scripts. + +Note: the lack of found security issues can either indicate that there +are none, or reveal that no-one ever bothered to find or publish them. + +### msgmerge + +`refreshpofiles()` runs this external program. + +* I was not able to crash it with `zzuf`. +* I could not find any past security hole. + +### msgfmt + +`isvalidpo()` runs this external program. + +* I was not able to make it behave badly using zzuf: it exits cleanly + when too many errors are detected. +* I could not find any past security hole. + +## po4a + +### Security history + +The only past security issue I could find in po4a is +[CVE-2007-4462](http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-4462): +`lib/Locale/Po4a/Po.pm` in po4a before 0.32 allowed local users to +overwrite arbitrary files via a symlink attack on the +gettextization.failed.po temporary file. + +This plugin would not have allowed to exploit this bug, as it does not +use, either directly or indirectly, the faulty `gettextize` function. + +Note: the lack of found security issues can either indicate that there +are none, or reveal that no-one ever bothered to find or publish them. + +### General feeling + +Are there any security issues on running po4a on untrusted content? + +To say the least, this issue is not well covered, at least publicly: + +* the documentation does not talk about it; +* grep'ing the source code for `security` or `trust` gives no answer. + +On the other hand, a po4a developer answered my questions in +a convincing manner, stating that processing untrusted content was not +an initial goal, and analysing in detail the possible issues. +The following analysis was done with his help. + +### Details + +* the core (`Po.pm`, `Transtractor.pm`) should be safe +* po4a source code was fully checked for other potential symlink + attacks, after discovery of one such issue +* the only external program run by the core is `diff`, in `Po.pm` (in + parts of its code we don't use) +* `Locale::gettext` is only used to display translated error messages +* Nicolas François "hopes" `DynaLoader` is safe, and has "no reason to + think that `Encode` is not safe" +* Nicolas François has "no reason to think that `Encode::Guess` is not + safe". The po plugin nevertheless avoids using it by defining the + input charset (`file_in_charset`) before asking `TransTractor` to + read any file. NB: this hack depends on po4a internals. + +#### Locale::Po4a::Text + +* does not run any external program +* only `do_paragraph()` builds regexp's that expand untrusted + variables; according to [[Joey]], this is "Freaky code, but seems ok + due to use of `quotementa`". + +#### Text::WrapI18N + +`Text::WrapI18N` can cause DoS +([Debian bug #470250](http://bugs.debian.org/470250)). +It is optional, and we do not need the features it provides. + +If a recent enough po4a (>=2009-01-15 CVS, which will probably be +released as 0.35) is installed, this module's use is fully disabled. +Else, the wiki administrator is warned about this at runtime. + +#### Term::ReadKey + +`Term::ReadKey` is not a hard dependency in our case, *i.e.* po4a +works nicely without it. But the po4a Debian package recommends +`libterm-readkey-perl`, so it will probably be installed on most +systems using the po plugin. + +`Term::ReadKey` has too far reaching implications for us to +be able to guarantee anything wrt. security. + +If a recent enough po4a (>=2009-01-15 CVS, which will probably be +released as 0.35) is installed, this module's use is fully disabled. + +#### Fuzzing input + +##### po4a-translate + +* po4a CVS 2009-01-16 +* Perl 5.10.0 + +`po4a-translate` uses more or less the same po4a features as our +`filter` function. + +Without specifying an input charset, same behaviour as +`po4a-gettextize`, so let's specify UTF-8 as input charset as of now. + +`LICENSES` is a 21M file containing 100 concatenated copies of all the +files in `/usr/share/common-licenses/`; I had no existing PO file or +translated versions at hand, which renders these tests +quite incomplete. + + zzuf -cv -s 0:10 -r 0.001:0.3 \ + po4a-translate -d -f text -o markdown -M utf-8 -L utf-8 \ + -k 0 -m LICENSES -p LICENSES.fr.po -l test.fr + +... seems to lose the fight, at the `readpo(LICENSES.fr.po)` step, +against some kind of infinite loop, deadlock, or any similar beast. + +The root of this bug lies in `Text::WrapI18N`, see the corresponding +section. + + +---- + +# Fixed holes + -- cgit v1.2.3