Server impersonation via mishandled host-key verification errors
Published Feb 18, 2025 · Updated Sep 2, 2026
Host-key verification bypass in OpenSSH 6.8p1 through 9.9p1 allows man-in-the-middle attackers to impersonate SSH servers. During DNS-based verification, sshkey_from_private returns an allocation error after attacker-driven memory exhaustion, but the caller treats any nonzero result as verified and skips remaining host-key checks. Exploitation requires an on-path position, VerifyHostKeyDNS set to yes or ask, and resource exhaustion; the accepted attacker key enables credential interception or session hijacking.
Summary
What happened
Host-key verification bypass in OpenSSH 6.8p1 through 9.9p1 allows man-in-the-middle attackers to impersonate SSH servers. During DNS-based verification, sshkey_from_private returns an allocation error after attacker-driven memory exhaustion, but the caller treats any nonzero result as verified and skips remaining host-key checks. Exploitation requires an on-path position, VerifyHostKeyDNS set to yes or ask, and resource exhaustion; the accepted attacker key enables credential interception or session hijacking.
The record
- CVE
- CVE-2025-26465
- Published
- Feb 18, 2025
- Updated
- Sep 2, 2026
- Vendor
- Siemens
- Product
- SIPLUS S7-1500 CPU 1518-4 PN/DP MFP
- Classifications
- CWE-390, T1557
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 18, 2025CVE publishedPublication date reported by the CVE source.
- Sep 2, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=V3.1.5 <*
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Qualys OpenSSH host-key verification bypass proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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