CVE-2026-98241 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
ipv6: xfrm: use full sockets in local error paths
xfrm6_local_rxpmtu() and xfrm6_local_error() dereference skb->sk as if it always pointed at a full IPv6 socket.
That is not guaranteed. TCP SYN-ACK skbs can be owned by a TCP_NEW_SYN_RECV request_sock while the output path itself is driven by the full listener. If rerouting selects an IPv6 XFRM tunnel route with a lower MTU, the local PMTU/error handling path can reach these callbacks with that mini-socket still attached to the skb.
The callbacks then miscast the request socket as a full inet/IPv6 socket and can read beyond the request_sock allocation when they access inet_sock or ipv6_pinfo state.
Resolve the owner with skb_to_full_sk() in both callbacks and bail out when no full socket is attached. This matches the surrounding XFRM IPv6 PMTU/error logic, which already reasons about full sockets with skb_to_full_sk().
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Analysis
by VulDB Data Team • 10/06/2026
The vulnerability identified within the Linux kernel's IPsec implementation involves a critical type confusion error in the handling of local network errors and Path Maximum Transmission Unit (PMTU) updates for IPv6 traffic. Specifically, the functions xfrm6_local_rxpmtu() and xfrm6_local_error(), which are responsible for processing PMTU notifications and local error conditions respectively, incorrectly assume that the socket pointer attached to a received packet buffer is always a fully initialized full socket structure. This assumption fails under specific network conditions where the kernel's routing logic selects an IPv6 XFRM tunnel route with a lower MTU than previously established or expected. In such scenarios, particularly during TCP connection establishment phases involving SYN-ACK packets, the socket associated with the packet may be a request_sock rather than a full inet_socket structure. The code proceeds to dereference this pointer as if it were a complete IPv6 socket object without verifying its actual type or integrity.
This misclassification leads directly to an out-of-bounds memory read vulnerability. When the callback functions attempt to access fields belonging to inet_sock or ipv6_pinfo structures, they are actually reading data from a much smaller request_sock allocation. Because the size and layout of these two structures differ significantly, accessing members that exist in the full socket but not in the request sock results in reading memory beyond the bounds of the allocated object. This out-of-bounds read can expose sensitive kernel memory contents to potential attackers who control or influence network traffic patterns. The flaw is particularly insidious because it relies on a race-like condition involving packet ownership and routing decisions, meaning it may only manifest under specific load conditions or during active connection setup processes where request sockets are prevalent.
From an operational impact perspective, this vulnerability allows for the leakage of kernel memory information, which can be leveraged by local attackers to bypass security mechanisms such as Kernel Address Space Layout Randomization (KASLR). By analyzing the leaked data, an attacker could determine the base addresses of critical kernel modules and functions, thereby facilitating further exploitation steps that require precise knowledge of kernel layout. While the immediate impact is information disclosure, this serves as a foundational step for more severe attacks including arbitrary code execution if combined with other vulnerabilities or heap spraying techniques. The issue affects systems running Linux kernels where IPv6 IPsec functionality is enabled and active traffic triggers PMTU discovery mechanisms over XFRM tunnels.
The resolution involves modifying the affected callbacks to utilize the skb_to_full_sk() helper function, which safely determines whether a packet buffer owns a full socket before proceeding with type-specific operations. If the function indicates that no full socket is attached, typically because the packet belongs to a request_sock or other non-full socket entity, the callback returns early without attempting further processing. This approach aligns with existing error handling logic within the XFRM IPv6 subsystem and ensures that only packets associated with fully initialized sockets are processed through paths expecting specific structure layouts. To mitigate this risk in environments where kernel updates may be delayed, administrators should consider disabling unnecessary IPsec tunneling configurations or restricting network access to prevent exploitation attempts until a patched version of the Linux kernel is deployed. This vulnerability corresponds to CWE-125 Out-of-bounds Read and falls under MITRE ATT&CK technique T1083 File and Directory Discovery when considering potential information gathering phases following successful memory disclosure.