CVE-2026-31668

A flaw was found in the Linux kernel's Segment Routing over IPv6 (SRv6) lightweight tunnel (seg6 lwtunnel). This component incorrectly shares a single destination cache between its input and output processing paths. This allows one path to reuse cached routing information populated by the other, bypassing its own independent routing context lookup. This can lead to unintended routing behavior or a bypass of network policy enforcement, potentially impacting network traffic integrity.

The patch fixes a routing logic flaw in the SRv6 seg6 lwtunnel implementation. Previously, each encap route had a single dst_cache stored in struct seg6_lwt. That cache was shared by both seg6_input_core and seg6_output_core. These two code paths may perform the post encapsulation SID lookup under different routing contexts such as rules that match on the ingress interface or VRF based table selection. With one shared cache, whichever path executed first populated the cache. The other path then reused the cached dst blindly and could bypass its own lookup. This is best classified as a logic or policy enforcement issue rather than memory corruption.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.