CVE-2026-55953: TLS 1.2 and DTLS client accepts unoffered anonymous cipher suite, bypassing server authentication

highCVSS 7.7CVE-2026-55953

CSIRTS triage

Authentication bypass

What: TLS 1.2 and DTLS client implementations incorrectly accept anonymous cipher suites that were not offered by the server, bypassing mutual authentication.
Who is affected: Applications using TLS 1.2 or DTLS clients that do not properly validate server cipher suite selection.
Urgency: High priority; allows server impersonation and man-in-the-middle attacks due to authentication bypass.
Action: Patch TLS/DTLS client to validate that accepted cipher suite was actually offered by server.

AI-assisted analysis generated from the source advisory — verify against the original.

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: high — CVSS 7.7
Published: 2026-08-06
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55953

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-559530.24% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 16% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-55953	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

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