CVE-2026-20004
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.
Published Mar 25, 2026 · corrected/updated Sep 28, 2026 · cisco ios xe · evidence confidence high
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 attempting Extensible Authentication Protocol (EAP) authentication when local EAP is enabled on an affected device or by using a machine-in-the-middle attack and resetting TLS connections between the affected device and other devices. A successful exploit could allow the attacker to exhaust the available memory on an affected device, resulting in an unexpected reload and a denial of service (DoS) condition.
Grounded briefings
Catalog interpretations for three audiences. Each brief cites ingested metadata and the original advisories below. They are not independent research and they do not invent exploit steps.
Executive
CVE-2026-20004 is a high public vulnerability record for cisco ios xe. It is not currently listed in the CISA Known Exploited catalog. Check the linked vendor or CERT advisories for patch status. This summary is a catalog interpretation of the ingested metadata and cites the original advisories below.
System administrator
Identify whether cisco ios xe is in your estate, then compare installed versions with the affected ranges. Affected packages or ranges on record: cisco/ios xe (16.9.1); cisco/ios xe (16.9.1a); cisco/ios xe (16.9.1b); cisco/ios xe (16.9.1s). Check the linked vendor or CERT advisories for patch status. Prefer the vendor or distribution advisory linked in Sources before changing production systems. This is a catalog interpretation, not a runbook.
Security analyst
Signals on file: CVSS 7.4, EPSS 0.2%. It is not currently listed in the CISA Known Exploited catalog. Weakness classes: CWE-771. Sources contributing to this record: cve_org, epss, nvd. Public exploit references, when present, are outbound links only and are not proof of active exploitation. This is a catalog interpretation of stored metadata.
Exploitation and remediation
Exploitation evidence
Not listed as known exploited in CISA KEV. Not in CISA KEV or VulnCheck KEV.
Patch and remediation
No required-action text is stored yet. Use the vendor or CERT links in Sources for patch availability.
Safe detection guidance
Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.
Technology hubs
Code
The project this record applies to. Exploit listings stay in References.
No public source repository is identified for this product.
Timeline
Detection, updates, and resolution for this record.
Mar 25, 2026 · NIST NVD
Detected
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 i
Sep 28, 2026 · NIST NVD
Updated
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 i
Affected
- cpe cisco/ios xe16.9.1
- cpe cisco/ios xe16.9.1a
- cpe cisco/ios xe16.9.1b
- cpe cisco/ios xe16.9.1s
- cpe cisco/ios xe16.9.2
- cpe cisco/ios xe16.9.3
- cpe cisco/ios xe16.9.3a
- cpe cisco/ios xe16.9.4
Sources
- CVE.orgVulnerability recordCVE-2026-20004
Official CVE identifier
cve.org - FIRST EPSSExploitation probabilityCVE-2026-20004
30-day exploitation probability 0.2%
first.org - NIST NVDVulnerability recordCVE-2026-20004
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 co
nvd.nist.gov