full-disclosure - Advisory 08/2004: Subversion remote vulnerability

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From: s.esser at e-matters.de (Stefan Esser)
Subject: Advisory 08/2004: Subversion remote vulnerability

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                           e-matters GmbH
                          www.e-matters.de

                      -= Security  Advisory =-



     Advisory: Subversion remote vulnerability
 Release Date: 2004/05/19
Last Modified: 2004/05/19
       Author: Stefan Esser [s.esser@...atters.de]

  Application: Subversion <= 1.0.2
     Severity: A vulnerability within Subversion allows remote 
               compromise of Subversion servers.
         Risk: Critical
Vendor Status: Vendor is releasing a bugfixed version.
    Reference: http://security.e-matters.de/advisories/082004.html


Overview:

   Quote from: http://subversion.tigris.org
   
   "The goal of the Subversion project is to build a version control system 
    that is a compelling replacement for CVS in the open source community. 
    The software is released under an Apache/BSD-style open source license.
   
    Features of Subversion
    
    * Most current CVS features
    * Directories, renames, and file meta-data are versioned
    * Commits are truly atomic
    * Apache network server option, with WebDAV/DeltaV protocol
    * Standalone server option
    * Branching and tagging are cheap (constant time) operations
    * Natively client/server, layered library design
    * Client/server protocol sends diffs in both directions
    * Costs are proportional to change size, not data size
    * Efficient handling of binary files
    * Parseable output"
    
   Subversion versions up to 1.0.2 are vulnerable to a date parsing 
   vulnerability which can be abused to allow remote code execution
   on Subversion servers and therefore could lead to a repository
   compromise.
      
   
Details:
   
   Similar to the libneon issue a manual scan for common programming errors
   revealed an unsafe call to sscanf() in one of Subversions date parsing
   functions.
   
   When Subversions tries to convert a string into an apr_time_t it falls
   back to the vulnerable sscanf() to decode old-styled date strings.
   This function is exposed to an external attacker through a DAV2 REPORT
   query or a get-dated-rev svn-protocol command.
   
   Both ways have been proven exploitable, but exploiting through the
   DAV2 protocol is somewhat harder because the date string has to be
   in utf-8 format. On the other hand exploiting through the svn-protocol
   is a trivial standard stackoverflow with the exception that whitespace
   and the '\0' character is forbidden.
   
   And as a sidenotice: Exploiting this stackoverflow is even possible
   when Propolice or similar protections are in place because a lot of
   fancy things can be done by overwriting the function parameters.
      

Proof of Concept:

   e-matters is not going to release an exploit for this vulnerability to
   the public.
   

Disclosure Timeline:

   02. May 2004 - Subversion developers and vendor-sec were notified 
                  by email
   03. May 2004 - Subversion vendor started their own analysis of the issue
                  and started compiling a list of big repositories to
		  receive pre-notifications
   11. May 2004 - Big subversion repositories (not already contacted
                  through vendor-sec) got pre-notified		  
   19. May 2004 - Coordinated Public Disclosure

   
CVE Information:

   The Common Vulnerabilities and Exposures project (cve.mitre.org) has
   assigned the name CAN-2004-0397 to this issue.


Recommendation:

   Exploiting this vulnerability on not heavily protected servers is trivial
   even for beginners, therefore it is strongly recommended to update
   immediately. Even Propolice users aren't safe because overwriting function
   arguments allows some fancy exploits.
   
   
GPG-Key:

   http://security.e-matters.de/gpg_key.asc
    
   pub  1024D/3004C4BC 2004-05-17 e-matters GmbH - Securityteam 
   Key fingerprint = 3FFB 7C86 7BE8 6981 D1DA  A71A 6F7D 572D 3004 C4BC


Copyright 2004 Stefan Esser. All rights reserved.

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-- 

--------------------------------------------------------------------------
 Stefan Esser                                        s.esser@...atters.de
 e-matters Security                         http://security.e-matters.de/

 GPG-Key                gpg --keyserver pgp.mit.edu --recv-key 0xCF6CAE69 
 Key fingerprint       B418 B290 ACC0 C8E5 8292  8B72 D6B0 7704 CF6C AE69
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