CVE-2026-20004: A vulnerability in the TLS library of Cisco IOS XE Software could allow an unauthenticated, adjacent attacker

Routine

HIGH 7.4MITIGATE

CVE-2026-20004 is a high-severity flaw (CVSS 7.4) affecting ios xe. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A vulnerability in the TLS library of Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to exhaust the available memory of an affected device. This vulnerability is due to improper management of memory resources during TLS connection setup. An attacker could exploit this vulnerability by repeatedly triggering the conditions that cause the memory increase. This could be done in a variety of ways, such as by repeatedly atte

Why this priority

High severity

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.4 (High)
Attack vector	Adjacent network
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 92%)
CISA exploited list	No
Weakness	CWE-771
Published	2026-03-25
Last modified	2026-09-28

Publisher (CNA): Cisco Systems, Inc. · Vendor: cisco

Last updated 2026-09-28 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-25 16:16 UTCPublished CVE record published
2026-09-28 15:18 UTCUpdated Record last modified

cisco ios xe MITIGATE

Affected: 16.9.1 · 16.9.1a · 16.9.1b · 16.9.1s · 16.9.2 · 16.9.3 · 16.9.3a · 16.9.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 16.9.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-20004?

ios xe: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-20004 being exploited?

CVE-2026-20004 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-20004 affect?

CVE-2026-20004 affects ios xe. Severity is high (CVSS 7.4). A vulnerability in the TLS library of Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to exhaust the available memory of an affected device. This vulnerability is due to improper management of memory resources dur

How urgent is CVE-2026-20004?

Priority 28/100. High severity

Software pages

iOS vulnerabilities · Cisco IOS XE vulnerabilities · Cisco vulnerabilities

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References

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