CVE-2026-63992 (CVSS 9.1)

Description

In the Linux kernel, the following vulnerability has been resolved: tunnels: do not assume transport header in iptunnel_pmtud_check_icmp() In some cases, iptunnel_pmtud_check_icmp() can be called while skb transport header is not set. This triggers an out-of-bound access, because (typeof(skb->transport_header))~0U is 65535. Access the icmp header based on IPv4 network header, after making sure icmp->type is present in skb linear part. Note that iptunnel_pmtud_check_icmpv6()) is fine.

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CVSS v3.1 Score

9.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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/43368636c663cff6e59dde93cf4b8e43ac28eb93 https://git.kernel.org/stable/c/509323077ef79a26ba0c60bb556e45c12c398b2d https://git.kernel.org/stable/c/5a92cb45e34749865d03daf8d3500f77b5f6644c https://git.kernel.org/stable/c/7f4f7efe7f30edd29c4988de01728bf2398217e4 https://git.kernel.org/stable/c/a096b6e34f602950af9a2b0856cd93a5f4c276d7 https://git.kernel.org/stable/c/c7b7ec3e69e673c0d6b57f74d21da50c485c598e https://git.kernel.org/stable/c/cb549df9ce4ee15c9d5b19ddab12cf2128e4313c https://git.kernel.org/stable/c/e917d0c69f01af2bb4fbea2b66d560a53b3ac7ec

Frequently Asked Questions

What is CVE-2026-63992? +

In the Linux kernel, the following vulnerability has been resolved: tunnels: do not assume transport header in iptunnel_pmtud_check_icmp() In some cases, iptunnel_pmtud_check_icmp() can be called while skb transport header is not set. This triggers an out-of-bound access, because (typeof(skb->transport_header))~0U is 65535. Access the icmp header based on IPv4 network header, after making sure icmp->type is present in skb linear part. Note that iptunnel_pmtud_check_icmpv6()) is fine. It has a CVSS v3.1 base score of 9.1 (CRITICAL).

How severe is CVE-2026-63992? +

CVE-2026-63992 has a CVSS v3.1 score of 9.1 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-2026-63992? +

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-2026-63992