CVE-2026-98401

A flaw was found in the Linux kernel's networking subsystem. When processing encapsulated network packets, the kernel fails to reset the transport header offset after stripping outer packet headers during tunnel decapsulation. A remote attacker could exploit this vulnerability by sending specially crafted encapsulated network traffic, triggering an out-of-bounds memory read that results in a kernel crash and a Denial of Service (DoS).

A stale transport header can remain in an skb after tunnel decapsulation when skb data is advanced to the inner frame but transport_header still refers to the removed outer transport header. If the inner GSO frame is forwarded at layer 2 through a bridge or HSR, the normal IP receive path does not reset the offset. qdisc_pkt_len_segs_init can then interpret the negative transport offset as a very large unsigned header length and perform an out of bounds read, causing a KASAN fault, page fault, or kernel crash. Exploitation requires several conditions including tunnel encapsulation, GSO metadata, layer 2 forwarding, and qdisc processing, so AC:H is appropriate. For the CVSS the PR:N value is used because a network peer that can send suitable traffic to an exposed tunnel endpoint does not need an authenticated local user context on the target. AV:A is used because practical triggering depends on access to the relevant tunnel or virtual network path and on locally generated GRO or GSO metadata rather than arbitrary Internet traffic. Impact is primarily denial of service. The paranoid score allows limited confidentiality impact because an out of bounds kernel read occurs, but no disclosure channel, write primitive, UAF, or privilege escalation path is established.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.