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Vulnerability of Apache log4j: memory leak via MDC and ThreadLocal

Synthesis of the vulnerability 

When an application uses an org.apache.log4j.MDC object, an attacker can call it to generate a memory leak, leading to a denial of service.
Vulnerable software: log4j.
Severity of this announce: 1/4.
Creation date: 29/05/2012.
Références of this computer vulnerability: 50486, VIGILANCE-VUL-11659.

Description of the vulnerability 

The org.apache.log4j.MDC (Mapped Diagnostic Context) class is used to process logs coming from different sources, in a multi-thread environment.

The MDC.remove() method deletes the context. However, it does not call the ThreadLocalMap.remove() method to free local variables of ThreadLocal.

When an application uses an org.apache.log4j.MDC object, an attacker can therefore call it to generate a memory leak, leading to a denial of service.
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This security vulnerability impacts software or systems such as log4j.

Our Vigil@nce team determined that the severity of this computer weakness bulletin is low.

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

An attacker with a expert ability can exploit this security note.

Solutions for this threat 

Apache log4j: version 1.2.17.
The version 1.2.17 is corrected:
  http://logging.apache.org/log4j/1.2/
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