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CVE-2026-63994

9.8 · CRITICAL

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()…

Published Jul 19, 2026EPSS 0.51%

Overview

CVE-2026-63994 is a critical-severity vulnerability. It was published on July 19, 2026 and has a CVSS 3.1 base score of 9.8 (CRITICAL).

This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refgit.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11Refgit.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7Refgit.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789bRefgit.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934Refgit.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4Refgit.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cffRefgit.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1Refgit.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43

How CyberStrike helps

Frequently asked questions

What is CVE-2026-63994?

CVE-2026-63994 is a critical-severity vulnerability. It was published on July 19, 2026 and has a CVSS 3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-63994?

This vulnerability has a CVSS 3.1 base score of 9.8, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-63994?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-63994?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-63994 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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