CVE-2026-64551

In the Linux kernel, the following vulnerability has been resolved:

sctp: validate STALE_COOKIE cause length before reading staleness

When an ERROR chunk with a STALE_COOKIE cause is received in the

COOKIE_ECHOED state, sctp_sf_do_5_2_6_stale() reads the 4-byte Measure

of Staleness that follows the cause header:

err = (struct sctp_errhdr *)(chunk->skb->data);

stale = ntohl(*(__be32 *)((u8 *)err + sizeof(*err)));

err is the first cause in the chunk, not the STALE_COOKIE cause that

caused the dispatch, and nothing guarantees the staleness field is

present. sctp_walk_errors() only requires a cause to be as long as the

4-byte header, so for a STALE_COOKIE cause of length 4 the read runs

past the cause, and for a minimal ERROR chunk past skb->tail. The value

is echoed to the peer in the Cookie Preservative of the reply INIT,

leaking uninitialized memory.

sctp_sf_cookie_echoed_err() already walks to the STALE_COOKIE cause, so

check its length there and pass it to sctp_sf_do_5_2_6_stale(), which

reads that cause instead of the first one. A STALE_COOKIE cause too

short to hold the staleness field is discarded.

The read is reachable by any peer that can drive an association into

COOKIE_ECHOED, including an unprivileged process using a raw SCTP socket

in a user and network namespace.