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Linux KernelOperating system · Linux

CVE-2026-31668

CRITICAL · 9.8 CVSS v3.1 Published 2026-04-24
Fix available
A fix is available. Upgrade to 5.10.253 / 5.15.203 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The seg6 lwtunnel in the Linux kernel uses a single dst_cache shared between seg6_input_core() and seg6_output_core(). Since these paths can operate in different routing contexts (e.g., different ingress interfaces or VRF tables), whichever path executes first populates the cache and the other path reuses it blindly, bypassing its own routing lookup. This allows traffic to circumvent IP rules and VRF table separation.

MitigationApply the kernel patch that splits the dst_cache into separate cache_input and cache_output structures, ensuring each path maintains its own independent cached destination.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 4.10.1, < 5.10.253>= 5.11, < 5.15.203>= 5.16, < 6.1.169>= 6.2, < 6.6.135>= 6.7, < 6.12.82>= 6.13, < 6.18.23>= 6.19, < 6.19.13= 4.10= 7.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check kernel version
    Run `uname -r` to get the running kernel version and compare against affected ranges: 4.10, 4.10.1 to < 5.10.253, 5.11 to < 5.15.203, 5.16 to < 6.1.169, 6.2 to < 6.6.135, 6.7 to < 6.12.82, 6.13 to < 6.18.23, 6.19 to < 6.19.13, and 7.0
    Affected if The installed kernel version falls within any of the affected version ranges listed in the CVE
  2. Verify SEG6 kernel module is loaded
    Run `lsmod | grep -i seg6` or check if SEG6 is built into the kernel by examining /boot/config-$(uname -r) for CONFIG_IPV6_SEG6_LWTUNNEL or similar SEG6 configuration options
    Affected if The seg6 kernel module is loaded or SEG6 is enabled in the kernel configuration (this is a prerequisite for the vulnerability to be exploitable)
  3. Check for active SEG6 tunnels or policies
    Run `ip -6 ru show` and `ip -6 seg6 tunnel show` (or `ip -6 sr policy show`) to list any configured IPv6 segment routing tunnels or policies
    Affected if There are active SEG6 tunnels or policies configured on the system, indicating the vulnerable code paths may be exercised
  4. Check for VRF or multiple routing table usage
    Run `ip vrf show` or check for multiple routing tables in use via `cat /etc/iproute2/rt_tables` and inspect whether the system uses VRF or policy routing with `ip -6 rule show`
    Affected if VRF instances or multiple routing contexts (policy routing) are configured, which creates the condition where the shared dst_cache causes routing bypass between different contexts

A system is affected if it runs a vulnerable kernel version AND has SEG6 functionality enabled AND uses VRF or multiple routing contexts, allowing the shared dst_cache to cause traffic to bypass routing rules.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.10.253 / 5.15.203 / 6.1.169 or later
Fixed in 5.10.2535.15.2036.1.169
Vendor patch git.kernel.org →
Interim mitigation

Apply the kernel patch that splits the dst_cache into separate cache_input and cache_output structures, ensuring each path maintains its own independent cached destination.

Recommended fix High confidence

Upgrade to kernel >=6.1.169 (LTS) or >=6.6.135 (latest stable), depending on distribution support

  1. 1. Identify the current running kernel version using `uname -r`
  2. 2. Determine the appropriate upgrade target based on your distribution's kernel packages: for 5.10.x branch upgrade to >=5.10.253, for 5.11-5.15.x upgrade to >=5.15.203, for 5.16-6.1.x upgrade to >=6.1.169, or for 6.2-6.6.x upgrade to >=6.6.135
  3. 3. For Debian/Ubuntu: Run `apt update && apt list --upgradable | grep linux-image` to see available kernel upgrades, then `apt install linux-image-<version>`
  4. 4. For RHEL/CentOS: Run `yum check-update` and `yum update kernel`
  5. 5. For Alpine: Run `apk update` and `apk upgrade linux-lts` or specify the exact version
  6. 6. After installation, reboot the system to load the patched kernel: `systemctl reboot`
  7. 7. Verify the fix is applied by checking the kernel version after reboot with `uname -r` and confirming it matches a fixed version
Caveat Kernel upgrades may require reboot and could introduce compatibility issues with custom kernel modules or older drivers; test in staging first

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Linux Kernel Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-31668 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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