CVE-2021-1616

MediumCVSS 4.7/10Last modified Jun 17, 2026

Description

A vulnerability in the H.323 application level gateway (ALG) used by the Network Address Translation (NAT) feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to bypass the ALG. This vulnerability is due to insufficient data validation of traffic that is traversing the ALG. An attacker could exploit this vulnerability by sending crafted traffic to a targeted device. A successful exploit could allow the attacker to bypass the ALG and open connections that should not be allowed to a remote device located behind the ALG. Note: This vulnerability has been publicly discussed as NAT Slipstreaming.

Metrics

CVSS 3.1 4.7/10CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N

Weakness enumeration

CWE-693

Affected software

No affected versions have been published.

Timeline

Published: Sep 23, 2021
Last modified: Jun 17, 2026
NVD status: Modified

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