Authentication algorithm downgrade via rogue extension negotiation
Published Nov 14, 2023 · Updated Feb 25, 2026
Insufficient message authenticity checks in AsyncSSH 2.14.0 and earlier allow man-in-the-middle attackers to downgrade client authentication. The SSH client handshake accepts an attacker-injected, unauthenticated SSH_MSG_EXT_INFO packet and uses its server-sig-algs value after the legitimate packet is deleted. An attacker positioned on the network path can replace the server's extension negotiation and force selection of a weaker authentication algorithm such as SHA-1.
Summary
What happened
Insufficient message authenticity checks in AsyncSSH 2.14.0 and earlier allow man-in-the-middle attackers to downgrade client authentication. The SSH client handshake accepts an attacker-injected, unauthenticated SSH_MSG_EXT_INFO packet and uses its server-sig-algs value after the legitimate packet is deleted. An attacker positioned on the network path can replace the server's extension negotiation and force selection of a weaker authentication algorithm such as SHA-1.
The record
- CVE
- CVE-2023-46445
- Published
- Nov 14, 2023
- Updated
- Feb 25, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-345, T1557
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Nov 14, 2023CVE publishedPublication date reported by the CVE source.
- Feb 25, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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What is affected?
Affected products and versions are unavailable in this record.
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
- Rogue extension negotiation proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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