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CVE-2026-55967: AES-GCM streaming APIs do not reject >64 GiB cumulative single messages, enabling counter wrap and keystream reuse

highCVSS 7.5CVE-2026-55967

CSIRTS triage

Other
What
The AES-GCM streaming APIs do not reject messages larger than 64 GiB, which can lead to counter wrap and keystream reuse.
Who is affected
Deployments using AES-GCM streaming APIs.
Urgency
Remediation is urgent due to the potential for cryptographic vulnerabilities, although exploitation has not been reported.
Action
Review and update the implementation of AES-GCM streaming APIs.

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 7.5
Published
2026-06-09
Exploitation
Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55967

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.

Referenced CVEs

CVECSIRTS overviewExternal
CVE-2026-55967coverage & exploitation statusNVD · CVE.org

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