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Vulnerability of ModSecurity: bypassing via Chunked

Synthesis of the vulnerability 

An attacker can use HTTP Chunked data, in order to bypass ModSecurity rules.
Vulnerable systems: Apache httpd Modules ~ not comprehensive, Debian, Fedora, openSUSE.
Severity of this threat: 2/4.
Creation date: 01/04/2014.
Références of this weakness: CVE-2013-5705, DSA-2991-1, FEDORA-2014-4633, FEDORA-2014-4720, MDVSA-2014:081, MDVSA-2015:106, openSUSE-SU-2014:0969-1, openSUSE-SU-2014:1047-1, VIGILANCE-VUL-14504.

Description of the vulnerability 

The HTTP Transfer-Encoding header can use the "chunked" type, to indicate that data is split in chunks before being transmitted.

However, if an attacker uses the "Chunked" (C uppercase) type, ModSecurity does not recognize it, but Apache httpd accepts it.

An attacker can therefore use HTTP Chunked data, in order to bypass ModSecurity rules.
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This weakness alert impacts software or systems such as Apache httpd Modules ~ not comprehensive, Debian, Fedora, openSUSE.

Our Vigil@nce team determined that the severity of this computer vulnerability note is medium.

The trust level is of type confirmed by the editor, with an origin of internet client.

A proof of concept or an attack tool is available, so your teams have to process this alert. An attacker with a technician ability can exploit this security bulletin.

Solutions for this threat 

ModSecurity: version 2.7.6.
The version 2.7.6 is fixed:
  http://www.modsecurity.org/

ModSecurity: patch for Chunked.
A patch is available in information sources.

Debian: new modsecurity-apache packages.
New packages are available:
  Debian 7: modsecurity-apache 2.6.6-6+deb7u2

Fedora: new mod_security packages.
New packages are available:
  Fedora 19: mod_security 2.7.5-3.fc19
  Fedora 20: mod_security 2.7.5-3.fc20

Mandriva BS2: new apache-mod_security packages.
New packages are available:
  Mandriva BS2: apache-mod_security 2.7.5-4.1.mbs2

Mandriva: new apache-mod_security packages.
New packages are available:
  Mandriva ES5: apache-mod_security 2.5.12-0.6mdvmes5.2
  Mandriva BS1: apache-mod_security 2.6.3-5.4.mbs1

openSUSE 11.4: new apache 2.2 packages.
New packages are available:
  openSUSE 11.4: apache2 2.2.17-80.1

openSUSE: new apache2-mod_security2 packages.
New packages are available:
  openSUSE 13.1: apache2-mod_security2 2.8.0-4.4.1
  openSUSE 12.3: apache2-mod_security2 2.7.5-2.10.1
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