CVE-2026-63992
Published Jul 19, 2026
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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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.
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.