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.
Weakness
The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Libssh2 | Libssh2 | * | 1.11.1 (including) |
| Red Hat Hardened Images | RedHat | libssh2-main-1.11.1-8.hum1 | * |
| Libssh2 | Ubuntu | devel | * |
| Libssh2 | Ubuntu | noble | * |
| Libssh2 | Ubuntu | questing | * |
| Libssh2 | Ubuntu | resolute | * |
| Libssh2 | Ubuntu | upstream | * |