Vulnerability details
CVE-2026-55199
libssh2 libssh2
libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler
CVSS 4.0
8.2High
Official description
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 scores
| Score | Version | Source | Vector |
|---|---|---|---|
| 8.2High | 4.0 | CVEProject cvelistV5 (CNA) (VulnCheck) | 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 |
| 5.9Medium | 3.1 | CVEProject cvelistV5 (CNA) (VulnCheck) | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
Affected products
| Vendor | Product | Versions | Source |
|---|---|---|---|
| libssh2 | libssh2 | v ≤ 1.11.1 | CVEProject cvelistV5 (CNA) |
References and advisories
3
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Details
- Published
- 2026-06-17
- Last updated
- 2026-11-08
- State
- Published
- Assigner (CNA)
- VulnCheck
Exploit prediction (EPSS)
0.91%
Probability of exploitation in 30 days
60.4%
Percentile (among all CVEs)
SSVC assessment (CISA)
- Automatable
- No
- Exploitation
- None
- Technical impact
- Partial
Weaknesses (CWE)
- CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')