CVE-2026-66033
Publication date 24 July 2026
Last updated 4 September 2026
Ubuntu priority
Medium
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| libssh2 | 26.04 LTS resolute |
Fixed 1.11.1-1ubuntu0.26.04.4
|
| 24.04 LTS noble |
Fixed 1.11.0-4.1ubuntu0.24.04.4
|
|
| 22.04 LTS jammy |
Needs evaluation
|
|
| 20.04 LTS focal |
Needs evaluation
|
|
| 18.04 LTS bionic |
Needs evaluation
|
|
| 16.04 LTS xenial |
Needs evaluation
|
|
| 14.04 LTS trusty |
Needs evaluation
|
Patch details
For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?
| Package | Patch details |
|---|---|
| libssh2 |
|
Severity score breakdown
CVSS version:
Base score 8.7 · High
Vector: 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
Base score 7.5 · High
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
References
Related Ubuntu Security Notices (USN)
- USN-8722-1
- libssh2 vulnerabilities
- 3 September 2026