Executive brief
A vulnerability exists in the Linux kernel's implementation of the TCP Authentication Option (TCP-AO), a security feature used to protect network traffic from tampering. Because the system compares security codes (MACs) in a way that takes different amounts of time depending on the data, an attacker could potentially use timing measurements to bypass authentication. This could allow an attacker to inject malicious data into network streams or disrupt communications.
Technical details
A side-channel vulnerability exists in net/ipv4/tcp_ao.c within the Linux kernel. The function tcp_ao_verify_hash used standard memcmp() to compare the received MAC with the calculated hash, which is not constant-time. This allows a remote attacker to perform a timing attack to recover the MAC or keying material, potentially leading to the bypass of TCP-AO protections. The fix replaces memcmp() with crypto_memneq() to ensure the comparison time does not vary based on the number of matching bytes. Patches have been released for multiple stable kernel branches including 6.12.y, 6.18.y, and 6.19.y.
Affected products
- Linux Linux Kernel 6.7 to 6.12.78, 6.13 to 6.18.19, 6.19 to 6.19.9, 7.0-rc1 to 7.0-rc2
Timeline
- 2026-03-02: other: Patch authored by Eric Biggers
- 2026-05-08: disclosed: CVE published
- 2026-05-08: advisory