CVE-2026-66033
libssh2 Integer Underflow DoS via AES-GCM Cipher Negotiation
CVSS Score
7.5
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-191 CWE-125 |
| Vendor | libssh2 |
| Product | libssh2 |
| Published | Jul 24, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High
Affected Versions
libssh2 / libssh2
0 ≤ 1.11.1
References
Credits
VladimirEliTokarev