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CVE Record

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

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.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A Linux Segment Routing IPv6 flaw can reuse routing information from the wrong traffic direction. On systems using seg6 encapsulation with interface-based rules or VRFs, this may bypass intended routing separation and misdirect traffic across security boundaries. The supplied CVSS rating is 9.8, but exposure depends on this specialized networking feature being configured.

Executive priority

Treat as urgent for Linux systems providing Segment Routing IPv6, VRF isolation, or policy routing. Rapidly establish whether seg6 is configured, then patch affected infrastructure. Avoid assuming every Linux host faces equal risk; the described flaw depends on specialized routing configuration.

Technical view

The seg6 lightweight tunnel implementation shares one destination cache between input and output processing. Because those paths may resolve a post-encapsulation SID under different routing contexts, the first path can populate a destination that the other reuses without its required lookup. The cited fix separates input and output caches.

Likely exposure

Likely exposure is concentrated in Linux hosts using seg6 lightweight-tunnel encapsulation, especially with ingress-interface routing rules or VRF table separation. Ordinary Linux systems not using this feature are less likely to be exposed. The supplied version data is ambiguous, so distribution-specific advisories should determine affected packages.

Exploitation context

The supplied record is not marked as included in CISA KEV, and no cited source establishes active exploitation or a public exploit. The CVSS vector describes network reachability without privileges or user interaction, but the provided technical description does not establish a practical end-to-end attack scenario.

Researcher notes

The security failure is cross-context destination-cache reuse, not a conventional memory-corruption issue. Assessment should examine whether input and output paths can resolve the same post-encapsulation SID differently. The bundle supplies multiple stable-tree commits but no authoritative per-distribution package mapping or demonstrated exploit chain.

Mitigation direction

  • Update to a vendor-supported kernel containing the applicable upstream fix.
  • Prioritize routers, gateways, and hosts configured for seg6 lightweight-tunnel encapsulation.
  • Review vendor advisories to map distribution kernel versions to the cited fixes.
  • Where operationally acceptable, disable unused seg6 configurations until patched.

Validation and detection

  • Inventory kernels and distribution package versions across potentially exposed systems.
  • Identify configured seg6 encapsulation routes and Segment Routing IPv6 usage.
  • Check for interface-dependent IP rules or VRFs intersecting those routes.
  • Confirm the installed kernel includes the applicable cache-separation fix.
  • Retest routing isolation between input and output contexts after remediation.
Prepared
Confidence
medium
Sources
10

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2026-31668 mapping review

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.8 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
0ADP providers
9Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Linux

Vulnerability scoring details

Base CVSS 3.1 score

9.8Critical
CVSS 3.1 vector shape for CVE-2026-31668Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux6c8702c60b88651072460f3f4026c7dfe2521d12, 6c8702c60b88651072460f3f4026c7dfe2521d12, 6c8702c60b88651072460f3f4026c7dfe2521d12, 6c8702c60b88651072460f3f4026c7dfe2521d12, 6c8702c60b88651072460f3f4026c7dfe2521d12, 6c8702c60b88651072460f3f4026c7dfe2521d12, 6c8702c60b88651072460f3f4026c7dfe2521d12, 6c8702c60b88651072460f3f4026c7dfe2521d12unaffected
LinuxLinux4.10, 0, 5.10.253, 5.15.203, 6.1.169, 6.6.135, 6.12.82, 6.18.23, 6.19.13, 7.0affected
Weakness

CWE details

No CWE listed

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