CVE-2026-98123sctp: fix soft lockup from unpadded ASCONF-ACK parameter iteration

Official description

In the Linux kernel, the following vulnerability has been resolved: sctp: fix soft lockup from unpadded ASCONF-ACK parameter iteration sctp_verify_asconf() walks ASCONF-ACK parameters with sctp_walk_params(), which advances by SCTP_PAD4(length), while the consumer sctp_get_asconf_response() iterates the same parameters advancing by the raw length, without padding. A single odd-length parameter desynchronises the two walks and makes the consumer interpret attacker-controlled bytes at a misaligned offset. When those bytes yield a length of zero, the while loop over asconf_ack_len makes no progress, spinning forever in softirq context, and the watchdog reports a soft lockup. All reads stay within the received skb, so the lockup is a pure remote denial of service. A remote peer can trigger it with a crafted ASCONF-ACK on an ADD-IP enabled association with an outstanding ASCONF (RFC 5061 section 4.1.2 requires the chunk to be authenticated, but the predefined empty key id 0 allows the peer to compute the same association HMAC from publicly exchanged parameters, so the gate does not help). The SCTP_PARAM_ERR_CAUSE case of sctp_verify_asconf() also performs no length check, letting a parameter without a complete error header reach the consumer, which reads errhdr.cause past the end of the parameter, an out-of-bounds read. Reject SCTP_PARAM_ERR_CAUSE parameters shorter than sizeof(struct sctp_addip_param) + sizeof(struct sctp_errhdr) at the verifier, and advance the consumer iterator with the same padding rule as the verifier to keep the two walks in lockstep. The verifier change guarantees a complete error header in every ERR_CAUSE parameter the consumer can see, so the consumer's asconf_ack_len check is dropped and it returns err_param->cause directly. The consumer padding fix is still required because odd lengths remain valid for SCTP_PARAM_ERR_CAUSE per RFC 5061. The issue was found by ZeroHive, a vulnerability hunting agent at Tencent Yunding Lab.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ba54cad229977f4fae6355dbdaf117088414fdd0
• https://git.kernel.org/stable/c/7d8e7ab6a0665888beee91f7ad77ac805963c4fd
• https://git.kernel.org/stable/c/5fbc6a778d5fce7628821236972596acb18e1065
• https://git.kernel.org/stable/c/4548d843e7b29f6d150d8caae4e64015fa226b0c
• https://git.kernel.org/stable/c/abf59d7f6fff23227256e8199aca5ade45758f8b
• https://git.kernel.org/stable/c/3be02999ab9131a4b96eb1eda4ca48b1cea80f03
• https://git.kernel.org/stable/c/7ba84e2971d208a2d6413a334ec28a8a32cdce0f
• https://git.kernel.org/stable/c/2cb0b0b1ed69430bf73740377ea0a1c44c50db63