# CVE-2026-72021: ipvs: use parsed transport offset in SCTP state lookup

> Incorrect SCTP state tracking in Linux kernel IPVS for IPv6 packets with extension headers causes improper connection state transitions and counter updates.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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:** 15 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-72021, DEBIAN-CVE-2026-72021, GHSA-vp82-2jx6-f675, UBUNTU-CVE-2026-72021

## What is CVE-2026-72021?

CVE-2026-72021 is a high-severity vulnerability in Linux, published on 15 Aug 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:

ipvs: use parsed transport offset in SCTP state lookup

set_sctp_state() reads the SCTP chunk header again in order to drive the
IPVS SCTP state table. For IPv6 it computes the offset with
sizeof(struct ipv6hdr), while the surrounding IPVS code uses iph.len from
ip_vs_fill_iph_skb(), where ipv6_find_hdr() has already skipped
extension headers and found the real transport header.

This makes the state machine read from the wrong offset for IPv6 SCTP
packets that carry extension headers. For example, an INIT packet with an
8-byte destination options header can be scheduled correctly by
sctp_conn_schedule(), but set_sctp_state() reads the first byte of the
SCTP verification tag as a DATA chunk type. The connection then moves
from NONE to ESTABLISHED instead of INIT1, gets the longer established
timeout, and updates the active/inactive destination counters
incorrectly. This happens even though the SCTP handshake has not
completed.

Use the parsed transport offset passed down from ip_vs_set_state() for
the SCTP chunk-header lookup. For IPv4 and IPv6 packets without
extension headers this preserves the existing offset.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-72021?


## How do I fix CVE-2026-72021?

Apply the vendor's patch.

## Is CVE-2026-72021 being exploited?

There is no known exploitation of CVE-2026-72021 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72021 and fix it if it is affected.

What it is: CVE-2026-72021 is a high-severity vulnerability in Linux, published on 15 Aug 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-2026-72021 in the wild and no public exploit code.

Affected product: Linux. 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-2026-72021/ (Markdown: https://insights.sbomify.com/CVE-2026-72021/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72021
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72021
- OSV: https://osv.dev/vulnerability/CVE-2026-72021

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72021/
Summaries are generated and may contain mistakes; the official description above is the record.