# CVE-2026-43139: xfrm6: fix uninitialized saddr in xfrm6_get_saddr()

> An attacker can read uninitialized kernel memory via IPv6 XFRM lookups, potentially exposing sensitive data.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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:** 6 May 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-43139, DEBIAN-CVE-2026-43139, GHSA-hr53-gf94-w7mp, ROOT-OS-DEBIAN-11-CVE-2026-43139, ROOT-OS-UBUNTU-2204-CVE-2026-43139, ROOT-OS-UBUNTU-2404-CVE-2026-43139, UBUNTU-CVE-2026-43139

## What is CVE-2026-43139?

CVE-2026-43139 is a high-severity vulnerability in Linux kernel, published on 6 May 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 uninitialized saddr in xfrm6_get_saddr()

xfrm6_get_saddr() does not check the return value of
ipv6_dev_get_saddr(). When ipv6_dev_get_saddr() fails to find a suitable
source address (returns -EADDRNOTAVAIL), saddr->in6 is left
uninitialized, but xfrm6_get_saddr() still returns 0 (success).

This causes the caller xfrm_tmpl_resolve_one() to use the uninitialized
address in xfrm_state_find(), triggering KMSAN warning:

=====================================================
BUG: KMSAN: uninit-value in xfrm_state_find+0x2424/0xa940
 xfrm_state_find+0x2424/0xa940
 xfrm_resolve_and_create_bundle+0x906/0x5a20
 xfrm_lookup_with_ifid+0xcc0/0x3770
 xfrm_lookup_route+0x63/0x2b0
 ip_route_output_flow+0x1ce/0x270
 udp_sendmsg+0x2ce1/0x3400
 inet_sendmsg+0x1ef/0x2a0
 __sock_sendmsg+0x278/0x3d0
 __sys_sendto+0x593/0x720
 __x64_sys_sendto+0x130/0x200
 x64_sys_call+0x332b/0x3e70
 do_syscall_64+0xd3/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable tmp.i.i created at:
 xfrm_resolve_and_create_bundle+0x3e3/0x5a20
 xfrm_lookup_with_ifid+0xcc0/0x3770
=====================================================

Fix by checking the return value of ipv6_dev_get_saddr() and propagating
the error.

Weakness: CWE-908 (Use of Uninitialized Resource), CWE-457 (Use of Uninitialized Variable)

## Which versions are affected by CVE-2026-43139?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43139?

Apply the vendor's patch.

## Is CVE-2026-43139 being exploited?

There is no known exploitation of CVE-2026-43139 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-2026-43139 and fix it if it is affected.

What it is: CVE-2026-43139 is a high-severity vulnerability in Linux kernel, published on 6 May 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-2026-43139 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-2026-43139/ (Markdown: https://insights.sbomify.com/CVE-2026-43139/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43139
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43139
- OSV: https://osv.dev/vulnerability/CVE-2026-43139

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43139/
Summaries are generated and may contain mistakes; the official description above is the record.