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

> Remote attackers can cause a kernel soft lockup and denial of service by sending crafted SCTP ASCONF-ACK chunks to Linux systems.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-104796, BELL-CVE-2026-98123, DEBIAN-CVE-2026-98123, GHSA-f2r5-8634-vv9q, UBUNTU-CVE-2026-98123

## What is CVE-2026-98123?

CVE-2026-98123 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### 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.

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2026-98123?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-98123?

Apply the vendor's patch.

## Is CVE-2026-98123 being exploited?

There is no known exploitation of CVE-2026-98123 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98123 and fix it if it is affected.

What it is: CVE-2026-98123 is a medium-severity denial of service vulnerability in Linux kernel, published on 25 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98123 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98123/ (Markdown: https://insights.sbomify.com/CVE-2026-98123/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98123
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98123
- OSV: https://osv.dev/vulnerability/CVE-2026-98123

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98123/
Summaries are generated and may contain mistakes; the official description above is the record.