Bug 2461759 (CVE-2026-31685)

Summary: CVE-2026-31685 kernel: netfilter: ip6t_eui64: reject invalid MAC header for all packets
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's netfilter component. This vulnerability occurs because the `eui64_mt6()` function, which processes IPv6 packets, does not properly validate the MAC header for all packets. Specifically, packets with a zero fragment offset could bypass an existing guard, allowing the system to attempt to access an invalid MAC header. A remote attacker could exploit this by sending specially crafted IPv6 packets, potentially causing a system crash and leading to a Denial of Service (DoS).
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-04-25 09:01:41 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: ip6t_eui64: reject invalid MAC header for all packets

`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 existing guard only rejects an invalid MAC header when
`par->fragoff != 0`. For packets with `par->fragoff == 0`, `eui64_mt6()`
can still reach `eth_hdr(skb)` even when the MAC header is not valid.

Fix this by removing the `par->fragoff != 0` condition so that packets
with an invalid MAC header are rejected before accessing `eth_hdr(skb)`.
Comment 1 Alexander B 2026-04-27 10:24:39 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026042545-CVE-2026-31685-3fcc@gregkh/T