Critical

Linux kernel netfilter ip6t_eui64 invalid MAC header handling flaw

IdentifiersCVE-2026-31685CWE-20

CVE-2026-31685 is a vulnerability in the Linux kernel netfilter ip6t_eui64 component. The vulnerable function, eui64_mt6(), derives a modified EUI-64 from the Ethernet source address and compares it with the low 64 bits of the IPv6 source address. The flaw is caused by insufficient validation of the packet's MAC header before accessing Ethernet header data via eth_hdr(skb). Specifically, the existing guard rejected an invalid MAC header only when par->fragoff != 0. For packets where par->fragoff == 0, eui64_mt6() could still reach eth_hdr(skb) even when the MAC header was invalid. The fix removes the par->fragoff != 0 condition so that all packets with an invalid MAC header are rejected before eth_hdr(skb) is accessed.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can cause the kernel to process a packet with an invalid MAC header in the ip6t_eui64 match path, potentially resulting in a kernel crash, denial of service, or other unintended kernel behavior during IPv6 netfilter processing. Available scoring also indicates potential confidentiality and integrity impact, but the provided content does not include a more specific demonstrated exploitation outcome beyond unsafe access to Ethernet header data.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, reduce exposure of vulnerable systems to untrusted IPv6 traffic that can traverse netfilter rules using the ip6t_eui64 match. Limit or disable use of the ip6t_eui64 match where operationally feasible, restrict network paths from untrusted sources, and apply filtering or segmentation to reduce attacker reachability until patched kernels can be deployed. Specific temporary mitigations beyond patching are not provided in the source content.

Remediation

Patch, then assume compromise.

Upgrade to a Linux kernel version containing the upstream fix for CVE-2026-31685. The remediation is to remove the par->fragoff != 0 condition in the validation logic so packets with invalid MAC headers are always rejected before eth_hdr(skb) is accessed. The provided content lists fixed package versions in multiple SUSE product lines, including kernel-default >= 6.12.0-160000.33.1 for SLES 16.0-related products, >= 6.4.0-150600.23.112.1 for SLES 15 SP6-related products, >= 5.14.21-150500.55.166.1 for SLES 15 SP5-related products, >= 5.14.21-150400.24.219.1 for SLES 15 SP4-related products, >= 4.12.14-122.310.1 for SLES 12 SP5-related products, and >= 3.0.101-108.210.1 for SLES 11 SP4 LTSS Extreme Core.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

LinuxLinux Kerneloperating_system

Rocky LinuxRocky Linuxoperating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

11 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

11 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity2

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-31685

NVD

nvd.nist.gov/vuln/detail/CVE-2026-31685

MITRE CWE · CWE-20

cwe.mitre.org

Patch

git.kernel.org/stable/c/288138418bef956f8b295751a4536c60f0e89f4a

Patch

git.kernel.org/stable/c/309ae3e9a51a69699ca94eac5fac5688fa562d55

Patch

git.kernel.org/stable/c/807d6ee15804df6f01a35c910f09612e858739a6

Patch

git.kernel.org/stable/c/9eda5478746ef7dc0e4e537b5a5e4b0ca1027091

Patch

git.kernel.org/stable/c/fdce0b3590f724540795b874b4c8850c90e6b0a8

git.kernel.org

git.kernel.org/stable/c/4d75bc2cd093bf5803edf512c099bfb220fd6459

git.kernel.org

git.kernel.org/stable/c/7d6a57411caf54df025860c9b1a82cd42d57a562

git.kernel.org

git.kernel.org/stable/c/d5603591373441fecf9951833d6d873e09320f08