Vulnerability Description
libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Libssh2 | Libssh2 | <= 1.11.1 |
Related Weaknesses (CWE)
References
- https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2Patch
- https://github.com/libssh2/libssh2/pull/2401Issue TrackingPatch
- https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cPatchThird Party Advisory
FAQ
What is CVE-2026-66033?
CVE-2026-66033 is a vulnerability with a CVSS score of 7.5 (HIGH). libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server t...
How severe is CVE-2026-66033?
CVE-2026-66033 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-66033?
Check the references section above for vendor advisories and patch information. Affected products include: Libssh2 Libssh2.