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vulnerability note CVE-2012-4557

Apache httpd: denial of service via mod_proxy_ajp

Synthesis of the vulnerability

When a Web server is made of Apache httpd with mod_proxy_ajp and a Tomcat server, an attacker can send a request requiring much processing time, in oder to make httpd disconnect the Tomcat server.
Vulnerable systems: Debian, HP-UX, openSUSE, RHEL.
Severity of this threat: 3/4.
Consequences of a hack: denial of service on service.
Pirate's origin: internet client.
Creation date: 30/11/2012.
Références of this weakness: 871685, BID-56753, c03734195, c03820647, CVE-2012-4557, DSA-2579-1, HPSBUX02866, openSUSE-SU-2013:0243-1, openSUSE-SU-2013:0248-1, RHSA-2013:0512-02, SSRT101139, VIGILANCE-VUL-12194.

Description of the vulnerability

The mod_proxy module provides a generic proxy service for Apache httpd. The mod_proxy_ajp module adds the AJP13 (Apache JServe Protocol version 1.3) support, which is used with Tomcat.

The mod_proxy_ajp module manage a list of Tomcat servers that it forwards requests to, with their state (working or not). When a Tomcat server does not reply at all or send an invalid response, the module marks it as not working. However, the fonction ajp_ilink_receive() in the file modules/proxy/ajp_link.c does not distinguish between time out (error code APR_TIMEUP) and faultly responses (error code AJP_ENO_HEADER). So, a time-out makes the httpd module considers that the Tomcat process is faultly.

When a Web server is made of Apache httpd with mod_proxy_ajp and a Tomcat server, an attacker can therefore send a request requiring much processing time, in oder to make httpd disconnect the Tomcat server.
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