CVE-2026-72250: netfilter: nf_conntrack_reasm: guard mac_header adjustment after IPv6 defrag
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nfconntrackreasm: guard macheader adjustment after IPv6 defrag
nfctfrag6reasm() slides the packet head forward to drop the IPv6 fragment header and then unconditionally advances skb->macheader:
skb->macheader += sizeof(struct fraghdr);
On the NFINETLOCALOUT defrag path the skb has no link-layer header yet, so skb->macheader is still the "not set" sentinel (u16)~0U. Adding sizeof(struct fraghdr) wraps it to a small value (0xffff + 8 == 7), after which skbmacheaderwasset() wrongly reports a MAC header is present and skbmacheader() points into the headroom.
The reassembler has done this unconditional add since it was introduced; it was harmless while macheader was a bare pointer, but wrong once macheader became a u16 offset whose unset state is the ~0U sentinel tested by skbmacheaderwasset(). The sibling net/ipv6/reassembly.c does the same relocation and does guard the adjustment; mirror the guard here.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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linux/Kernelto a version that resolves this vulnerability.Fixed in 5.10.261 - Upgrade
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ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-38.38.1 - Compensating control
In netfilter IPv6 defragmentation (nf_ct_frag6_reasm()), guard the skb->mac_header adjustment with a check that the MAC header is set before executing skb->mac_header += sizeof(struct frag_hdr).
Event History
Frequently Asked Questions
What is the severity of CVE-2026-72250?
CVE-2026-72250 has a risk score of 23, indicating a critical severity level.
How do I fix CVE-2026-72250?
To mitigate CVE-2026-72250, update the Linux kernel to the patched version that addresses the vulnerability.
What systems are affected by CVE-2026-72250?
CVE-2026-72250 affects Linux kernel versions prior to the release that includes the fix for this vulnerability.
What are the potential consequences of CVE-2026-72250?
The vulnerability could lead to improper handling of IPv6 fragments, potentially allowing for packet manipulation.
Who is responsible for resolving CVE-2026-72250?
The Linux kernel maintainers are responsible for addressing CVE-2026-72250 through updates and patches.