CVE-2026-31637

Vulnerability

The Linux kernel's rxrpc subsystem contains a flaw in the rxkad_decrypt_ticket() function, which decrypts RXKAD response tickets but fails to verify whether the decryption succeeded via crypto_skcipher_decrypt(). When decryption fails, the parser still processes the decrypted buffer as plaintext, enabling an attacker to inject controlled data into the ticket parsing logic [1][2][3][4].

Exploitation

A remote attacker can send a malformed RESPONSE packet with a non-block-aligned ticket length, causing the decryption operation to fail. Despite the failure, the kernel continues to parse the buffer, treating attacker-controlled bytes as a legitimate ticket [1]. No authentication or user interaction is required, making this vulnerability exploitable over the network with low complexity, as reflected by the CVSS score of 9.8.

Impact

Successful exploitation allows an attacker to drive the ticket parser with arbitrary data, potentially leading to memory corruption, privilege escalation, or denial of service within the kernel's rxrpc context. Given the critical severity, this could result in full system compromise.

Mitigation

The issue is resolved by checking the decrypt result and aborting the connection with RXKADBADTICKET when decryption fails [1][2][3][4]. The fix has been incorporated into stable Linux kernel branches; users should update to the latest kernel version containing the patch.