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Date: Tue, 27 Jan 2015 11:02:11 -0500 (EST)
From: cve-assign@...re.org
To: Salvatore Bonaccorso <carnil@...ian.org>
cc: oss-security@...ts.openwall.com,
        Assign a CVE Identifier <cve-assign@...re.org>
Subject: Re: [perl #119505] Segfault from bad backreference


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().

---

CVE assignment team, MITRE CVE Numbering Authority M/S M300
202 Burlington Road, Bedford, MA 01730 USA
[ PGP key available through http://cve.mitre.org/cve/request_id.html ]

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