CVE-2026-55952: TLS 1.3 server denial of service via malformed ClientHello pre-shared key extension

unknownCVE-2026-55952

CSIRTS triage

Denial of service

What: Malformed ClientHello pre-shared key extension can cause a denial of service.
Who is affected: Deployments using TLS 1.3 are affected.
Urgency: Remediation is necessary due to the potential for denial of service, although severity is currently unknown.
Action: Review and validate ClientHello configurations to prevent malformed requests.

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

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: unknown
Published: 2026-07-02
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55952

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-2026-559520.49% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 39% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-55952	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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A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

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