CVE-2021-1616

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

MEDIUM
4.7
CVSS Score
Published: September 23, 2021 at 02:30 AM UTC
Updated: June 17, 2026 at 03:32 AM UTC
1 product affected across 1 vendorIOS Xe

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Severity
MEDIUM4.7
Exploit prediction
EPSS 1%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 17.6.1
Affected range stops below 17.6.1, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

4.7MEDIUMcisco
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-693NVD-CWE-Other

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