Executive brief
OpenSSH is a widely used tool for secure remote access to servers. A configuration flaw in versions prior to 10.3 causes the software to incorrectly interpret settings meant to restrict specific encryption algorithms (ECDSA). Instead of allowing only the chosen algorithms, the system may permit any available ECDSA algorithm, potentially allowing connections using weaker encryption than intended by the administrator.
Technical details
A logic error in OpenSSH's configuration parsing (sshd_config) affects how ECDSA algorithms are handled in PubkeyAcceptedAlgorithms and HostbasedAcceptedAlgorithms. If a user specifies a single ECDSA algorithm (e.g., ecdsa-sha2-nistp384), the parser misinterprets this as a wildcard, enabling all supported ECDSA algorithms. This bypasses intended cryptographic restrictions set by administrators. The vulnerability is reachable over the network without authentication, though exploitation depends on the specific security policy the administrator intended to enforce. The issue is resolved in OpenSSH version 10.3.
Affected products
- OpenBSD OpenSSH before 10.3
Timeline
- 2026-04-02: disclosed: OpenSSH 10.3 release announcement
- 2026-04-02: patched: Fixed in OpenSSH 10.3
- 2026-04-02: advisory