CVE-2021-1616 - CVE House
Back to Database
Status published Medium CVE-2021-1616

Cisco IOS XE Software H.323 Application Level Gateway Bypass Vulnerability

Vulnerability 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.

Impact Analysis

Refer to official advisory for detailed impact metrics.

Remediation

Ensure systems are updated to the latest vendor-supplied patch levels.

THREAT MONITOR

Am I Vulnerable?

Launch our assessment wizard to check if your infrastructure is exposed to • CVE-2021-1616

Credits & Attribution

No credits recorded in the NVD database.

References

More from Cisco

View All →
CVE-2025-20393
Cisco Secure Email Gateway and Cisco Secure Email and Web Manager Remote Command Execution Vulnerability
Critical 10
CVE-2025-20377
Cisco Unified Intelligence Center API Information Disclosure Vulnerability
Medium 4.3
CVE-2025-20376
Cisco Unified Contact Center Express Remote Code Execution Vulnerability
Medium 6.5
CVE-2025-20375
Cisco Unified Contact Center Express Arbitrary File Upload Vulnerability
Medium 6.5
CVE-2025-20374
Cisco Unified Contact Center Express Arbitrary File Download Vulnerability
Medium 4.9

Affected Vendor

Affected Software

Cisco IOS XE Software
Vulnerable Versions:
Unknown

Timeline

Official Publish: September 23rd, 2021
Last Modified: November 7th, 2024
Added to House: July 21st, 2026

CVSS Vectors

V3: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N

Weaknesses (CWE)

CWE-693

MITRE ATT&CK TTPs

T1562 Impair Defenses
Defense Evasion
T1190 Exploit Public-Facing Application
Initial Access
T1068 Exploitation for Privilege Escalation
Privilege Escalation
T1550 Use Alternate Authentication Material
Defense Evasion
T1485 Data Destruction
Impact