Federico Kirschbaum has reported a vulnerability in ZyXEL ZyNOS, which can be exploited by malicious people to cause a DoS (Denial of Service).

The vulnerability is caused due to an error in the handling of malformed fragmented IP packets. This can be exploited to cause a vulnerable router to consume a large amount of CPU resources.

The vulnerability has been reported in Prestige 650R-31 running ZyNOS FW 3.40 (KO.1). Other Prestige routers and versions of ZyNOS may also be affected.

NOTE: According to the original advisory, the vulnerability was only tested on the local interface. It is therefore not currently known whether the external interface also is affected.

Solution
Update the firmware to version 3.40 (GT.5).

Provided and/or discovered by
Federico Kirschbaum

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