Linux kernel authencesn: out-of-place decrypt writes high-order sequence bits into the destination buffer

Impact

The authencesn AEAD template stored the high-order IPsec sequence bits at the end of the destination buffer during out-of-place decryption, where they do not belong, and hashed the wrong layout. On a GPU node this is a local memory-corruption primitive in core kernel crypto code, reachable by any process that can open an AF_ALG socket or drive an IPsec SA using an esn AEAD - which on a shared node includes unprivileged tenant workloads inside containers, since AF_ALG needs no capability by default. NVD scores it as local privilege escalation with high confidentiality, integrity and availability impact (7.8), so the realistic worst case is a tenant process corrupting kernel memory and escaping the container to host root on a node that holds other tenants' GPUs. The upstream record is a fix description only; no exploit or crash report is published, so treat reachability as plausible rather than demonstrated.

Who can reach it

Local, authenticated as any user on the node. A process that can create an AF_ALG socket for an authencesn(...) algorithm, or configure an ESN IPsec SA, reaches the path. No management-network or remote access is needed; no GPU privileges are needed.

What to do

Take the stable kernel update that carries the fix (five stable branches have backports, listed in the record) and reboot the node. There is no module reload or runtime mitigation for an in-kernel crypto template, so this is a drain-and-reboot per node. As a stopgap on nodes where tenants do not need it, blocking AF_ALG (seccomp or by not loading algif_aead) removes the unprivileged path, though it does not address IPsec use.

References

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