CVE-2026-31668: seg6: separate dst_cache for input and output paths in seg6 lwtunnel

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-24 · updated 2026-10-19
Weakness: CWE-459

Description

In the Linux kernel, the following vulnerability has been resolved: seg6: separate dst_cache for input and output paths in seg6 lwtunnel The seg6 lwtunnel uses a single dst_cache per encap route, shared between seg6_input_core() and seg6_output_core(). These two paths can perform the post-encap SID lookup in different routing contexts (e.g., ip rules matching on the ingress interface, or VRF table separation). Whichever path runs first populates the cache, and the other reuses it blindly, bypassing its own lookup. Fix this by splitting the cache into cache_input and cache_output, so each path maintains its own cached dst independently.

Affected products

Linux kernel: from 4.10.1 before 5.10.253; from 5.11 before 5.15.203; from 5.16 before 6.1.169; from 6.2 before 6.6.135; from 6.7 before 6.12.82; from 6.13 before 6.18.23 — fixed in 5.10.253, 5.15.203, 6.1.169, 6.12.82, 6.18.23, 6.19.13

How to fix

Upgrade to a fixed version: Linux kernel 5.10.253, 5.15.203, 6.1.169, 6.12.82. Check the vendor advisory for mitigations.

References

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