libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.
CVSS Details
- CVSS 4.0 Base Score: 8.2 (HIGH)
- CVSS 4.0 Vector: (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X)
- CVSS 3.1 Base Score: 7.5
- CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Alpine Linux | — | Upgrade libssh2Upgrade rust | Jun 24, 2026 | Jun 17, 2026 |
| Debian | — | Upgrade libssh2 | Jul 23, 2026 | Jul 23, 2026 |
| Gentoo Linux | — | Upgrade net-libs/libssh2. | Aug 20, 2026 | Aug 20, 2026 |
| Redhat_linux | — | No solution exists | Jul 17, 2026 | Jun 17, 2026 |
| Ubuntu | — | Upgrade libssh2-1t64 | Jun 30, 2026 | Jun 17, 2026 |
| Vmware Photon_os | — | Use 'tdnf update' to upgrade all packages to the latest version. | Jul 6, 2026 | Jun 17, 2026 |
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