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Cisco Bug: CSCvh73829 - Cisco Adaptive Security Appliance TCP Syslog Denial of Service Vulnerability

Last Modified

Apr 17, 2020

Products (1)

  • Cisco ASA 5500-X Series Firewalls

Known Affected Releases


Description (partial)

A vulnerability in the TCP syslog module of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to exhaust the 1550-byte buffers on an affected device, resulting in a denial of service (DoS) condition.

The vulnerability is due to a missing boundary check in an internal function. An attacker could exploit this vulnerability by establishing a man-in-the-middle position between an affected device and its configured TCP syslog server and then maliciously modifying the TCP header in segments that are sent from the syslog server to the affected device. A successful exploit could allow the attacker to exhaust buffer on the affected device and cause all TCP-based features to stop functioning, resulting in a DoS condition. The affected TCP-based features include AnyConnect SSL VPN, clientless SSL VPN, and management connections such as Secure Shell (SSH), Telnet, and HTTPS.

There are no workarounds that address this vulnerability.

This advisory is available at the following link:

This vulnerability affects ASA releases 9.6 and later with a TCP syslog server configured.

To determine, if your ASA has a TCP syslog server configured, use the show running-config | inc logging host command and look for lines referencing protocol 6 (i.e. TCP). The following example shows the output of the command for a device that has TCP syslog server configured:

ASA# show running-config | inc logging host
logging host Inside 6/1470
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