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computer vulnerability alert CVE-2009-1243

Linux kernel: denial of service via /proc/net/udp

Synthesis of the vulnerability

An attacker can read from /proc/net/udp in order to stop the system.
Vulnerable products: Linux.
Severity of this weakness: 1/4.
Consequences of a hack: denial of service on server.
Hacker's origin: user shell.
Creation date: 01/04/2009.
Références of this bulletin: BID-34329, BID-34333, CVE-2009-1243, VIGILANCE-VUL-8586.

Description of the vulnerability

The /proc/net/udp pseudo file indicates the list of listening UDP services or established UDP sessions (its content is equivalent to "netstat -aun").

To handle the various simultaneous access to this file, the kernel uses a lock. When the user requests a read() on this file, the kernel locks the access, sends the data, and unlock the access.

If the user requests a read() of zero byte on this file, the kernel does not need to lock the access. However, at the end of the call, it tries to unlock a lock which is not locked. This error stops the kernel.

An attacker can therefore read from /proc/net/udp in order to stop the system.
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