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CVSS 9.8 · CRITICAL

CVE-2026-63994

In the Linux kernel, the following vulnerability has been resolved: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]() Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head. Fix this possible UAF by initializing the local variables after the skb_cow() call. Remove skb_reset_network_header() calls which were not needed.

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Analysis

A critical Use-After-Free vulnerability has been identified in the Linux kernel's tunneling implementation. This flaw can be triggered during Path MTU Discovery, potentially allowing a remote attacker to cause a kernel crash or execute arbitrary code on the host system.

Relevant roles

LinuxCloudKubernetesDockerBackendCyberSecurity

Severity

Score: 9.8(CRITICAL)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
AV: NETWORK
AC: LOW
PR: NONE
UI: NONE
S: UNCHANGED
C: HIGH
I: HIGH
A: HIGH

EPSS

Probability of exploitation (next 30 days): 0.0018 (0.2%)
Percentile: 7.4%
EPSS: 2026-07-20

Technical description

In the Linux kernel, the following vulnerability has been resolved: tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]() Sashiko found that iptunnel_pmtud_build_icmp() and iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr() before an skb_cow() call which can reallocate skb->head. Fix this possible UAF by initializing the local variables after the skb_cow() call. Remove skb_reset_network_header() calls which were not needed.

Published: 7/19/2026, 4:17:38 PM
Last modified: 7/20/2026, 3:17:01 PM

References

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