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Cisco Bug: CSCuo37957 - ATTN-3-SYNC_TIMEOUT - IOS-XE CPU Resource Consumption Vulnerability

Last Modified

Oct 03, 2019

Products (1)

  • Cisco ASR 1000 Series Aggregation Services Routers

Known Affected Releases


Description (partial)

A vulnerability in the packet reassembly subsystem of Cisco IOS-XE could allow an unauthenticated, remote attacker to consume CPU resources which may lead to a denial of service (DoS) condition.

The vulnerability is due to an error message that is triggered to both the console and syslog when a fragmented packet can not be properly reassembled.  When an affected device fails to successfully perform reassembly, instead of silently dropping the fragments an error message of ATTN-3-SYNC_TIMEOUT may be triggered.  On a device that is highly loaded, this may be leveraged to consume CPU resources that may be required by another process resulting in a temporary halt of the queued process.  In some situations this may lead to a drop of transit traffic.  An attacker could trigger this vulnerability by sending a series of IPv4 or IPv6 fragments directly to the affected device that are designed to trigger the error message.

Cisco IOS-XE devices rate limit error messages to once every 60 seconds by default.

Cisco ASR 1000, Cisco CSR 1000V, or Cisco ISR 4400 series devices running an affected version of Cisco IOS-XE are vulnerable.
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