High [CVE-2026-20004] Cisco IOS XE Software TLS Memory Exhaustion Denial of Service Vulnerability
This high-severity Cisco advisory covers CVE-2026-20004 affecting Cisco IOS XE Software 16.9.2, Cisco IOS XE Software 16.9.1a, Cisco IOS XE Software 16.9.1b.
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Summary
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 att…
Affected products named by the advisory: Cisco IOS XE Software 16.9.2; Cisco IOS XE Software 16.9.1a; Cisco IOS XE Software 16.9.1b; Cisco IOS XE Software 16.9.1s; and 3 more.
- Scope: This vulnerability affects Cisco devices that are running a vulnerable release of Cisco IOS XE Software if they are configured with features that may establish TLS connections, including but not limited to:
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Mitigation checklist
- There are no workarounds that address this vulnerability.
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
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