# CVE-2026-89783: xfrm6: fix out-of-bounds write in xfrm6_input_addr() when secpath is full

> An off-by-one error in the Linux kernel IPv6 XFRM input path allows an out-of-bounds write, potentially causing a kernel panic and denial of service.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101337, BELL-CVE-2026-89783, DEBIAN-CVE-2026-89783, GHSA-w5hj-mmmx-p42j, UBUNTU-CVE-2026-89783

## What is CVE-2026-89783?

CVE-2026-89783 is a critical memory corruption vulnerability in Linux, published on 16 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:

xfrm6: fix out-of-bounds write in xfrm6_input_addr() when secpath is full

The depth check in xfrm6_input_addr() is off by one:

  if (1 + sp->len == XFRM_MAX_DEPTH)
          goto drop;
  ...
  sp->xvec[sp->len++] = x;

xfrm_input() can leave sp->len == XFRM_MAX_DEPTH, and the transport-mode
receive path re-enters IPv6 input via xfrm_trans_reinject() with that
secpath preserved. If the inner packet carries a destination-options HAO
option or a type-2 routing header, xfrm6_input_addr() is called with
sp->len == XFRM_MAX_DEPTH; the check (1 + 6 == 6) is false, so
sp->xvec[sp->len++] writes one slot past the 6-element xvec[]. The write
stays within the sec_path allocation (invisible to KASAN); UBSAN_BOUNDS
flags it and panics under panic_on_warn.

Use "sp->len >= XFRM_MAX_DEPTH", matching xfrm_input(). This also
restores one chain level the old check rejected at sp->len == 5.

  UBSAN: array-index-out-of-bounds in net/ipv6/xfrm6_input.c:309:10
  index 6 is out of range for type 'xfrm_state *[6]'

## Which versions are affected by CVE-2026-89783?


## How do I fix CVE-2026-89783?

Apply the vendor's patch.

## Is CVE-2026-89783 being exploited?

There is no known exploitation of CVE-2026-89783 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89783 and fix it if it is affected.

What it is: CVE-2026-89783 is a critical memory corruption vulnerability in Linux, published on 16 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-2026-89783 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-2026-89783/ (Markdown: https://insights.sbomify.com/CVE-2026-89783/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89783
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89783
- OSV: https://osv.dev/vulnerability/CVE-2026-89783

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89783/
Summaries are generated and may contain mistakes; the official description above is the record.