CVE-2026-98417 in Linux
Summary
by MITRE • 10/14/2026
In the Linux kernel, the following vulnerability has been resolved:
net: xfrm: reject unrepresentable espintcp transport headers
ESP-in-TCP can hand xfrm packets whose transport header offset no longer fits after the stream parser trims the TCP envelope. The plain transport header reset truncates that offset and triggers the skb warning path.
Use the careful transport-header helper and drop the skb through the existing XFRM error path when the offset cannot be represented.
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Analysis
by VulDB Data Team • 10/14/2026
The Linux kernel vulnerability identified in the net: xfrm subsystem involves a critical flaw within the ESP-in-TCP encapsulation mechanism, specifically concerning how transport header offsets are managed after TCP stream parsing operations. In normal network processing, packets traversing through IPsec with ESP-in-TCP encapsulation undergo several layers of decapsulation and re-encapsulation. The core issue arises when the kernel's stream parser trims the outer TCP envelope from an incoming packet to expose the inner payload. This trimming operation modifies the internal state of the socket buffer (skb), particularly affecting how offsets for subsequent protocol headers are calculated and stored.
The technical flaw lies in the handling of the transport header offset following this trimming process. When the TCP envelope is removed, the resulting plain transport header reset fails to correctly account for the change in packet structure, leading to a situation where the recorded transport header offset no longer accurately represents its position within the modified skb. This misalignment causes the kernel's internal consistency checks to fail, triggering an skb warning path that indicates an unrepresentable or invalid state. Such warnings are not merely informational; they signal a potential for undefined behavior, memory corruption, or denial of service if the malformed packet continues through further processing stages without proper validation and rejection.
From an operational impact perspective, this vulnerability allows attackers to potentially trigger kernel warnings or crashes by crafting malicious ESP-in-TCP packets that exploit the offset miscalculation. While immediate remote code execution may not be guaranteed solely by this flaw, it creates a pathway for denial of service attacks against systems processing high volumes of IPsec traffic. The error path activation can lead to system instability, especially in environments where kernel warnings are configured to panic on certain conditions or when the vulnerability is chained with other issues to escalate privilege levels. This affects any Linux-based infrastructure relying heavily on ESP-in-TCP for secure communications over TCP ports such as 443, which is common in mobile and constrained network scenarios.
To mitigate this risk, developers have implemented a fix that utilizes a careful transport-header helper function designed to validate the integrity of header offsets before proceeding with further processing. When the offset cannot be correctly represented after the stream parser trims the TCP envelope, the system now explicitly drops the skb through an existing XFRM error path rather than allowing it to proceed in a corrupted state. This ensures that malformed packets are discarded safely without triggering kernel warnings or causing instability. Administrators should ensure their systems are updated with patches addressing this specific net: xfrm issue and monitor for any unusual network traffic patterns involving ESP-in-TCP encapsulation, particularly from untrusted sources. Regular application of security updates is essential to maintain the integrity of IPsec implementations within the Linux kernel environment.