In the Linux kernel, the following vulnerability has been resolved: netfilter: ip6t_eui64: reject invalid MAC header for all packets eui64_mt6()… (CVE-2026-31685)
A vulnerability in the Linux kernel's netfilter subsystem (ip6t_eui64) allowed packets with invalid MAC headers to be processed improperly due to insufficient validation. Specifically, the function eui64_mt6() did not reject invalid MAC headers for packets where the fragment offset was zero, potentially leading to improper access of Ethernet header data. This flaw has been fixed by removing the condition that exempted packets with zero fragment offset from validation, ensuring all packets with invalid MAC headers are rejected before processing. The vulnerability affects multiple Linux kernel versions prior to certain patched releases. A patch is available and has been incorporated into updated kernel packages. Users should update and reboot to apply the fix.
AI Analysis
Technical Summary
The Linux kernel netfilter ip6t_eui64 module contained a vulnerability where the function eui64_mt6() derived a modified EUI-64 from the Ethernet source address and compared it with the IPv6 source address's low 64 bits. The existing validation only rejected invalid MAC headers when the packet's fragment offset (par->fragoff) was non-zero. For packets with a zero fragment offset, the function could access the Ethernet header even if it was invalid, leading to potential security issues. The fix removes the par->fragoff != 0 condition, ensuring all packets with invalid MAC headers are rejected before eth_hdr(skb) is accessed. This vulnerability is tracked as CVE-2026-31685 and has a CVSS 3.1 score of 9.4 (critical severity). Multiple Linux kernel versions prior to the patched releases are affected. Ubuntu security advisories USN-8490-1 and USN-8491-1 provide details and updated kernel package versions addressing this and other kernel vulnerabilities.
Potential Impact
An attacker could exploit this vulnerability to cause improper processing of network packets with invalid MAC headers, potentially leading to system compromise. The CVSS score of 9.4 indicates high impact with network attack vector, low attack complexity, no privileges required, no user interaction, and high confidentiality and availability impact. The flaw could allow an attacker to compromise the system by exploiting the improper validation in the netfilter ip6t_eui64 module.
Mitigation Recommendations
A patch is available and has been released by vendors, including Ubuntu. Users should update their Linux kernel packages to the fixed versions listed in the Ubuntu advisories USN-8490-1 and USN-8491-1 and reboot their systems to apply the updates. Due to an ABI change, recompilation and reinstallation of third-party kernel modules may be required. Follow vendor instructions carefully to ensure full remediation.
In the Linux kernel, the following vulnerability has been resolved: netfilter: ip6t_eui64: reject invalid MAC header for all packets eui64_mt6()… (CVE-2026-31685)
Description
A vulnerability in the Linux kernel's netfilter subsystem (ip6t_eui64) allowed packets with invalid MAC headers to be processed improperly due to insufficient validation. Specifically, the function eui64_mt6() did not reject invalid MAC headers for packets where the fragment offset was zero, potentially leading to improper access of Ethernet header data. This flaw has been fixed by removing the condition that exempted packets with zero fragment offset from validation, ensuring all packets with invalid MAC headers are rejected before processing. The vulnerability affects multiple Linux kernel versions prior to certain patched releases. A patch is available and has been incorporated into updated kernel packages. Users should update and reboot to apply the fix.
CVSS v3.1
Score 9.4critical
Affected software
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protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=resolutepkg:deb/ubuntu/[email protected]?arch=source&distro=resoluteRun on your own infrastructure? 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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The Linux kernel netfilter ip6t_eui64 module contained a vulnerability where the function eui64_mt6() derived a modified EUI-64 from the Ethernet source address and compared it with the IPv6 source address's low 64 bits. The existing validation only rejected invalid MAC headers when the packet's fragment offset (par->fragoff) was non-zero. For packets with a zero fragment offset, the function could access the Ethernet header even if it was invalid, leading to potential security issues. The fix removes the par->fragoff != 0 condition, ensuring all packets with invalid MAC headers are rejected before eth_hdr(skb) is accessed. This vulnerability is tracked as CVE-2026-31685 and has a CVSS 3.1 score of 9.4 (critical severity). Multiple Linux kernel versions prior to the patched releases are affected. Ubuntu security advisories USN-8490-1 and USN-8491-1 provide details and updated kernel package versions addressing this and other kernel vulnerabilities.
Potential Impact
An attacker could exploit this vulnerability to cause improper processing of network packets with invalid MAC headers, potentially leading to system compromise. The CVSS score of 9.4 indicates high impact with network attack vector, low attack complexity, no privileges required, no user interaction, and high confidentiality and availability impact. The flaw could allow an attacker to compromise the system by exploiting the improper validation in the netfilter ip6t_eui64 module.
Mitigation Recommendations
A patch is available and has been released by vendors, including Ubuntu. Users should update their Linux kernel packages to the fixed versions listed in the Ubuntu advisories USN-8490-1 and USN-8491-1 and reboot their systems to apply the updates. Due to an ABI change, recompilation and reinstallation of third-party kernel modules may be required. Follow vendor instructions carefully to ensure full remediation.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-31685
- Osv Schema Version
- 1.7.0
- Ecosystems
- ["Ubuntu:Pro:14.04:LTS","Ubuntu:Pro:16.04:LTS","Ubuntu:16.04:LTS","Ubuntu:Pro:FIPS:16.04:LTS","Ubuntu:Pro:18.04:LTS","Ubuntu:18.04:LTS","Ubuntu:Pro:FIPS-updates:18.04:LTS","Ubuntu:Pro:FIPS:18.04:LTS","Ubuntu:Pro:20.04:LTS","Ubuntu:20.04:LTS","Ubuntu:Pro:FIPS-updates:20.04:LTS","Ubuntu:Pro:FIPS:20.04:LTS","Ubuntu:22.04:LTS","Ubuntu:Nvidia-BlueField:22.04:LTS","Ubuntu:Pro:FIPS-preview:22.04:LTS","Ubuntu:Pro:FIPS-updates:22.04:LTS","Ubuntu:Pro:Realtime:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:Nvidia-BlueField:24.04:LTS","Ubuntu:Pro:FIPS-updates:24.04:LTS","Ubuntu:Pro:Realtime:24.04:LTS","Ubuntu:25.10","Ubuntu:26.04:LTS"]
- Cvss Version
- 4.0
Threat ID: 6a58b4cc68715ace43dab04c
Added to database: 07/16/2026, 10:39:08 UTC
Last enriched: 08/01/2026, 04:58:48 UTC
Last updated: 09/14/2026, 22:01:33 UTC
Views: 20
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