Executive brief
A vulnerability in the Linux kernel's IPsec implementation could cause network communication failures when using specific security features. When Extended Sequence Number (ESN) and asynchronous authentication are enabled, the system incorrectly processes security headers, leading to 100% packet loss for encrypted traffic. This primarily impacts the availability of secure network connections and the reliability of VPN or encrypted tunnels.
Technical details
A logic error exists in the Linux kernel's XFRM subsystem (net/ipv4/ah4.c and net/ipv6/ah6.c) regarding the Authentication Header (AH) with Extended Sequence Number (ESN) support. When an asynchronous hash (ahash) implementation is used, the setup path correctly appends a 4-byte 'seqhi' slot for ESN, but the completion callbacks (ah_output_done and ah_input_done) fail to account for this offset. This causes the kernel to copy or compare the wrong bytes for the Integrity Check Value (ICV), resulting in authentication failures and total packet loss. The fix ensures the callback-side layout matches the setup path by correctly skipping the ESN seqhi slot.
Affected products
- Linux Linux kernel All versions supporting ESN in AH (IPv4/IPv6) prior to the fix
Timeline
- 2026-05-13: other: Patch authored
- 2026-05-28: disclosed: CVE published
References
- https://git.kernel.org/stable/c/0555d4f526232b3c9e3afbcd490c0c0793aefec6
- https://git.kernel.org/stable/c/2ffaa7a94f9a4d22724364a1821735a0231d9f8d
- https://git.kernel.org/stable/c/729899a2aa8bda7844be0cdcd3b470f11b912eda
- https://git.kernel.org/stable/c/7db99a09b3bc87268287bc7ab5f2e7f382b5ad87
- https://git.kernel.org/stable/c/ec54093e6a8f87e800bb6aa15eb7fc1e33faa524