Symptom
A vulnerability in the Session Initiation Protocol (SIP) ALG for the NAT feature of Cisco ASA Software and Cisco FTD Software could allow an unauthenticated, remote attacker to bypass the ALG and open unauthorized connections with a host located behind the ALG. The SIP ALG is enabled by default.
This vulnerability is due to insufficient traffic validation for the SIP ALG. An attacker could exploit this vulnerability by sending crafted SIP traffic through the ALG to a host located behind the security device. A successful exploit could allow the attacker to open unauthorized connections to the remote host and undertake actions leveraging that host.
This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-natalg-bypass-cpKGqkng
Conditions
Please refer to the Security Advisory.
Workaround
Please refer to the Security Advisory.
Further Problem Description
Please refer to the Security Advisory.
PSIRT Evaluation
The Cisco PSIRT has assigned this bug the following CVSS version 3 score. The Base CVSS score as of the time of evaluation is 4.7:
https://tools.cisco.com/security/center/cvssCalculator.x?vector=CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
CVE ID CVE-2021-34790 has been assigned to document this issue.
Additional information on Cisco's security vulnerability policy can be found at the following URL:
https://tools.cisco.com/security/center/resources/security_vulnerability_policy.html
