CVE-2026-66033: libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation
CSIRTS triage
- What
- An integer underflow vulnerability can lead to a denial of service via AES-GCM cipher negotiation.
- Who is affected
- Deployments of libssh2 are affected.
- Urgency
- Remediation is urgent due to the high severity of the vulnerability.
- Action
- Update to the latest version of libssh2 to mitigate the issue.
AI-assisted analysis generated from the source advisory — verify against the original.
⚡ Watch libssh2
Get an email when a new libssh2 advisory drops — max one per day, one-click unsubscribe.
Details
Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-66033
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-2026-660330.37% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 30% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2026-66033 | coverage & exploitation status | NVD · CVE.org |
Same CVEs, other sources
How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.
More from Microsoft Security Response Center
- highCVE-2026-57992: Microsoft Edge (Chromium-based) Remote Code Execution Vulnerability2026-07-14
- mediumCVE-2026-59926: Mistune: XSS via unescaped class option in Admonition directive2026-07-14
- mediumCVE-2026-55003: Windows Remote Desktop Protocol (RDP) Information Disclosure Vulnerability2026-07-14
- highCVE-2026-42900: Microsoft Windows App Store Elevation of Privilege Vulnerability2026-07-14
- unknownCVE-2026-13867: Chromium: CVE-2026-13867 Inappropriate implementation in Geolocation2026-07-14