CVE-2026-98371

Description

In the Linux kernel, the following vulnerability has been resolved: xfrm: iptfs: fix runt reassembly panic from short inner tot_len When the start of an inner packet is split across two outer packets such that fewer than 4 bytes land at the end of the first one, __input_process_payload() saves those bytes as a runt and skips the iplen/iphlen validation performed for in-place packets. When the continuation packet arrives, iptfs_reassem_cont() only requires the declared inner length to be >= sizeof(ra_runt) (6) before allocating the reassembly skb with that attacker-controlled length. However, __iptfs_iphlen() always returns the fixed minimum IP header size (20 for IPv4, 40 for IPv6), so for an inner IPv4 tot_len in [6, 19] the header-completion copy writes past the declared packet length, and the subsequent "ipremain -= copylen" underflows to ~4GB, leaving the payload copy length bounded only by blkoff (up to 64KB). At runtime the skb_put() tailroom check turns this into skb_over_panic(), i.e. an unprivileged kernel panic (DoS), reachable locally via userns+netns IPTFS SAs and remotely against IPTFS VPN gateways when the decrypted outer skb is linear (e.g. AF_PACKET taps, tun/tap delivery). Align the runt path with the normal path by requiring the declared inner length to cover at least the IP header size. This also subsumes the previous >= sizeof(ra_runt) check, since the minimum IP header is always larger than the runt buffer. This issue was found by the autokbug dynamic kernel fuzzer at Tencent Yunding Lab.

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EPSS — Exploit Prediction

0.0016

Probability of exploitation

0.05%

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/5b8afb56ccb7c014b0f1ac40341708b200443c2d https://git.kernel.org/stable/c/a7018ee0ea8622ed59edc064be4e0f2c26464f53 https://git.kernel.org/stable/c/dc33262be1fe43d0eb0b84fb58c6ed42e2f64a8c

Frequently Asked Questions

What is CVE-2026-98371? +

In the Linux kernel, the following vulnerability has been resolved: xfrm: iptfs: fix runt reassembly panic from short inner tot_len When the start of an inner packet is split across two outer packets such that fewer than 4 bytes land at the end of the first one, __input_process_payload() saves those bytes as a runt and skips the iplen/iphlen validation performed for in-place packets. When the continuation packet arrives, iptfs_reassem_cont() only requires the declared inner length to be >= sizeof(ra_runt) (6) before allocating the reassembly skb with that attacker-controlled length. However, __iptfs_iphlen() always returns the fixed minimum IP header size (20 for IPv4, 40 for IPv6), so for an inner IPv4 tot_len in [6, 19] the header-completion copy writes past the declared packet length, and the subsequent "ipremain -= copylen" underflows to ~4GB, leaving the payload copy length bounded only by blkoff (up to 64KB). At runtime the skb_put() tailroom check turns this into skb_over_panic(), i.e. an unprivileged kernel panic (DoS), reachable locally via userns+netns IPTFS SAs and remotely against IPTFS VPN gateways when the decrypted outer skb is linear (e.g. AF_PACKET taps, tun/tap delivery). Align the runt path with the normal path by requiring the declared inner length to cover at least the IP header size. This also subsumes the previous >= sizeof(ra_runt) check, since the minimum IP header is always larger than the runt buffer. This issue was found by the autokbug dynamic kernel fuzzer at Tencent Yunding Lab.

How do I check if I'm vulnerable to CVE-2026-98371? +

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.