CVE-2026-63994 (CVSS 9.8)

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.

Is your site exposed to CVE-2026-63994?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0052

Probability of exploitation

0.41%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

References

Other References

https://git.kernel.org/stable/c/50750d86a2e5266aba0c295483b3397843198b11 https://git.kernel.org/stable/c/6dff77899b9e9fe5d854abda3a98ad04e7229ef7 https://git.kernel.org/stable/c/7254aef4d1a7e18e887af9010e2f2dc34806789b https://git.kernel.org/stable/c/76cd9398a0470257ab765bdf5f358a2af2e17934 https://git.kernel.org/stable/c/95b6d772bfe788331d9742d73eaa12e113b2adc4 https://git.kernel.org/stable/c/b4bc94353050b1fa7b702bd4c6600710dd926cff https://git.kernel.org/stable/c/bf8b3f34c37c162357138e7c0942723b8b94fed1 https://git.kernel.org/stable/c/f3f204541f280a6ecb04503a0d6794d93990ca43

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-63994? +

CVE-2026-63994 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0052, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-63994? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

CVE-2026-63994