CVE-2026-55199
8.2
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
Summary
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.
Affected Software
| Vendor | Product | Version Range | Status |
|---|---|---|---|
| libssh2 | libssh2 | 0 <= 1.11.1 | affected |
| libssh2 | libssh2 | 17626857d20b3c9a1addfa45979dadcee1cd84a4 | unaffected |
Weaknesses
- CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')
ADP Enrichment
CISA ADP Vulnrichment
- SSVC:
- Exploitation: none
- Automatable: no
- Technical Impact: partial
References
- https://github.com/libssh2/libssh2/pull/1864
- https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4
- https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handler
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