Ed25519 Signature Handler Verification Flaws

PuTTY versions up to 0.83 contain a weak authentication vulnerability in the Ed25519 signature verification function (eddsa_verify in crypto/ecc-ssh.c) that allows remote attackers to potentially forge or manipulate digital signatures due to improper validation of Ed25519 signature components. While a public proof-of-concept exploit exists and the vulnerability affects signature verification, the real-world impact remains unproven, with CVSS 3.7 (low severity) and EPSS probability indicating exploitation is difficult and requires high complexity. The vendor (PuTTY developers) has already released a patch addressing this issue.

A cryptographic signature verification flaw exists in tinyssh's Ed25519 signature handler (crypto_sign_ed25519_tinyssh.c) that allows improper validation of signatures, potentially enabling an attacker to forge or bypass signature checks. Affected versions of janmojzis tinyssh up to 20250501 are impacted, with the vulnerability requiring local execution and high attack complexity. A public exploit has been disclosed, and vendor patches are available in version 20260301.