Re: [perl #119505] Segfault from bad backreference

[cve-assign () mitre org]

On Sat, 24 Jan 2015, Salvatore Bonaccorso wrote:

> Hi Kurt,
>
> On Fri, Jan 23, 2015 at 02:38:51PM -0700, Kurt Seifried wrote:
> > http://perl5.git.perl.org/perl.git/commitdiff/0c2990d652e985784f095bba4bc356481a66aa06
> >
> > The code that parses regex backrefs (or ambiguous backref/octal) such as
> > \123, did a simple atoi(), which could wrap round to negative values on
> > long digit strings and cause seg faults.
> >
> > Include a check on the length of the digit string, and if greater than 9
> > digits, assume it can never be a valid backref (obviating the need for
> > the atoi() call).
> >
> > I've also simplified the code a bit, putting most of the \g handling
> > code into a single block, rather than doing multiple "if (isg) {...}".
> >
> > PoC:
> >
> > https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=776046
> > perl -e '/\7777777777/'
> >
> > not sure if this can be exploited at all, but someone creative maybe has
> > ideas, if so this may need a CVE.
>
> Just additional infomration: I think this was way back found already
> around 2008, in opensuse-commits the following can be found:
>
> http://marc.info/?l=opensuse-commit&m=121933719424130
>
> then also reported in the Perl request-tracker at
>
> https://rt.perl.org/Public/Bug/Display.html?id=119505
>
> Regards,
> Salvatore

Use CVE-2013-7422 for the issue as disclosed in 
https://rt.perl.org/Public/Bug/Display.html?id=119505 for "Segfault in 
S_regmatch from bad backreference," as demonstrated using:

  ./perl -e '/\7777777777/'


The relationships between CVE-2013-7422 and this OpenSUSE commit are not 
immediately clear:

  http://marc.info/?l=opensuse-commit&m=121933719424130

This commit has both "fix regexp backref overflow crash [bnc#372331]" and, 
separately, "Fix another regexp backref overflow crash."  This suggests 
two separate bugs.

A test for perl-regexp-refoverflow.diff (regcomp.c) uses:

  perl -e '/\6666666666/'

but the code change casts atoi()'s return value to unsigned, whereas the 
CVE-2013-7422 commit uses different logic that minimizes use of atoi().

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