CVE-2026-66033
8.7
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Summary
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.
Affected Software
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| libssh2 | libssh2 | 0 <= 1.11.1 | affected |
| libssh2 | libssh2 | a2ed82d40964bbc0d64cd717aa0a5a892117d2e6 | unaffected |
Weaknesses
- CWE-191: Integer Underflow (Wrap or Wraparound)
- CWE-125: Out-of-bounds Read
References
- https://github.com/libssh2/libssh2/pull/2401
- https://github.com/libssh2/libssh2/commit/a2ed82d40964bbc0d64cd717aa0a5a892117d2e6
- https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation
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