CVE-2021-1616
MEDIUMDescription
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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
Exploit Intelligence
Moderate risk: more likely to be exploited than 65% of all known CVEs.
References
Related Vulnerabilities
Other CWE-693 (Protection Mechanism Failure) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2013-2465 | Critical | 9.8 | 99% | KEV + Ransom | - |
| CVE-2024-21412 | High | 8.1 | 95% | KEV + Ransom | Fix |
| CVE-2013-0431 | Medium | 5.3 | 90% | KEV + Ransom | - |
| CVE-2019-1003030 | Critical | 9.9 | 76% | KEV | - |
| CVE-2025-40536 | High | 8.1 | 72% | KEV | Fix |
| CVE-2025-0411 | High | 7.0 | 67% | KEV | Fix |
Common questions
How do I fix CVE-2021-1616?
Upgrade ios xe to 17.6.1 or later.
Is CVE-2021-1616 being actively exploited?
Not that we know of. CVE-2021-1616 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 1.2% is the estimated probability that it will be exploited in the next 30 days. That is higher than 65% of all scored CVEs.
How severe is CVE-2021-1616?
CVE-2021-1616 has a CVSS v3 base score of 4.7, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2021-1616 affect?
Published advisories record a fix for ios xe (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
Embed a live status badge for CVE-2021-1616
Markdown
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TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.
This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.