This security update addresses three OpenSSH vulnerabilities: a non-default GSSAPI Key Exchange flaw (CVE-2026-3497) allowing denial of service or code execution via client disconnection, and two issues (CVE-2025-61984 & CVE-2025-61985, CVSS 3.6 LOW) enabling potential code execution through malicious usernames or ssh:// URIs when used with ProxyCommand.
Jeremy Brown discovered that the OpenSSH GSSAPI Key Exchange incorrectly handled disconnecting clients. In non-default configurations where the GSSAPIKeyExchange setting is enabled, a remote attacker could use this issue to cause OpenSSH to crash, resulting in a denial of service, or possibly execute arbitrary code. (CVE-2026-3497) David Leadbeater discovered that OpenSSH incorrectly handled certain control characters in usernames. When untrusted usernames and the ProxyCommand are being used, an attacker could possibly use this issue to execute arbitrary code. (CVE-2025-61984) David Leadbeater discovered that OpenSSH incorrectly handled NULL characters in ssh:// URIs. When the ProxyCommand is being used, an attacker could possibly use this issue to execute arbitrary code. (CVE-2025-61985)