CVE-2026-53250

What it actually does

This is a time-of-check/time-of-use race condition in the Linux kernel AF_XDP transmit path. TX metadata stored in userspace-mapped UMEM can be modified concurrently by a userspace process while the kernel is validating and then later using checksum fields. Specifically, csum_start and csum_offset were read once for bounds checking and then read again for skb assignment; a malicious local process could change the values between those reads so that the values used by the kernel were not the values that passed validation. The result is a potential out-of-bounds memory access during transmit checksum computation. The most likely technical outcomes are kernel memory corruption, kernel crash, or denial of service; depending on kernel configuration, allocator state, and reachable code paths, privilege escalation cannot be ruled out, but no public exploit maturity is indicated.

Why it matters to the business

Successful exploitation could allow a local user or compromised workload with access to AF_XDP/UMEM transmit functionality to destabilize the host kernel, causing service interruption for workloads running on the affected system. In environments using high-performance packet processing, containers, network appliances, NFV platforms, or systems that expose packet-processing capabilities to less-trusted users, the operational risk is higher because a local crash can disrupt multiple services on the same host. This issue is not listed in CISA KEV, is not known to be used in ransomware campaigns, and has a very low EPSS score, so broad internet-scale exploitation is unlikely; however, kernel flaws still merit timely remediation because local attackers often chain them after initial access.

How an attack unfolds

An attacker first needs local code execution on a Linux system where they can use AF_XDP transmit functionality and create or interact with UMEM-backed packet buffers. They prepare TX metadata in the UMEM region with checksum metadata values that initially satisfy the kernel's bounds checks. While the kernel is processing the transmit path in xsk_skb_metadata(), the attacker races another write to the same userspace-mapped metadata and changes csum_start or csum_offset after validation but before the kernel assigns the values to the skb. The kernel then performs checksum work using the attacker-controlled post-validation values, potentially causing out-of-bounds memory access in the transmit path. A reliable exploit would need to win the race consistently and shape kernel memory behavior; the practical result may range from repeated kernel oops/panic to possible memory corruption useful in a chained local privilege escalation.

How to fix it

Upgrade to a Linux kernel build that includes the upstream fix for the AF_XDP xsk_skb_metadata() checksum metadata race, or apply the vendor backport for this CVE. The fix is to cache csum_start and csum_offset into local variables and use the same validated values for assignment. Because no exact fixed package versions were provided, use the relevant distribution or appliance vendor advisory to identify the corrected kernel package for each supported release. Where immediate patching is not possible, reduce exposure by limiting AF_XDP usage to trusted services, restricting CAP_NET_RAW and other network administration capabilities, preventing untrusted containers or users from creating AF_XDP sockets, disabling unnecessary high-performance packet-processing workloads, and applying least-privilege container runtime/seccomp/AppArmor/SELinux controls that block access to AF_XDP-related socket creation where feasible.

How to confirm the fix worked

Confirm that systems are running a kernel package containing the vendor fix or an upstream commit that changes xsk_skb_metadata() to read csum_start and csum_offset once into local variables before validation and assignment. Validate exposure by checking whether AF_XDP is enabled and whether any workloads create AF_XDP sockets or use XDP/UMEM transmit paths. On Linux hosts, inventory kernel versions with uname -r and package-manager metadata, then compare against vendor fixed releases. For source-based validation, inspect the kernel source or debug symbols for the affected xsk_skb_metadata() implementation. After patching, run regression tests for AF_XDP/XDP packet transmission and confirm no kernel oops, KASAN, UBSAN, or checksum-related warnings appear under normal packet-processing load.

Typical attack path

1. Gain local code execution on a Linux host, either as a user, compromised workload, or process with access to packet-processing capabilities.
2. Obtain the privileges or configuration needed to create/use AF_XDP sockets and UMEM-backed transmit buffers.
3. Create AF_XDP TX traffic with metadata containing checksum fields that initially pass kernel validation.
4. Continuously modify the shared UMEM metadata from userspace while the kernel processes transmit metadata.
5. Race the kernel between validation and use of csum_start/csum_offset so unchecked values are assigned to the skb.
6. Trigger checksum computation with the raced values, causing out-of-bounds kernel memory access and possible crash or memory corruption.

How to detect it

There is no reliable remote network indicator for this vulnerability because exploitation requires local interaction with AF_XDP/UMEM transmit metadata. To assess possible prior exploitation, review kernel logs, system journals, crash dumps, and monitoring telemetry for kernel oops, panic, KASAN, UBSAN, or general protection fault events around AF_XDP transmit activity. Useful sources include journald, /var/log/kern.log, /var/log/messages, dmesg output, kdump/vmcore artifacts, audit logs showing suspicious use of CAP_NET_RAW or CAP_NET_ADMIN, container runtime logs for privileged or network-capable containers, and EDR telemetry for unusual local programs creating AF_XDP sockets. Look for stack traces or warnings referencing xsk_skb_metadata(), AF_XDP, xsk, UMEM, skb checksum processing, csum_start, csum_offset, skb_checksum_help(), or transmit checksum offload paths. Because crashes may be indistinguishable from stability bugs, correlate kernel faults with newly executed local binaries, containers granted elevated networking capabilities, or abnormal high-rate AF_XDP TX activity.

• xsk_skb_metadata
• csum_start
• csum_offset
• AF_XDP
• XDP_UMEM
• UMEM
• skb_checksum_help
• skb_checksum
• BUG: KASAN
• KASAN: slab-out-of-bounds
• KASAN: out-of-bounds
• general protection fault
• kernel BUG
• kernel panic
• Oops:
• WARNING: CPU
• xsk
• af_xdp

What your security team should do

• Prioritize patching Linux hosts that run AF_XDP, XDP, DPDK-like packet processing, network appliances, NFV workloads, container networking components, or other high-throughput transmit paths.
• Treat this primarily as a local post-compromise kernel risk: focus on multi-tenant systems, container platforms, shared development hosts, and systems where untrusted users can run code.
• Inventory where AF_XDP sockets and UMEM-backed packet processing are used, and map those systems to the kernel versions provided by the OS or appliance vendor.
• Until patched, restrict CAP_NET_RAW/CAP_NET_ADMIN and block untrusted workloads from creating AF_XDP sockets using container runtime policies, seccomp, AppArmor, SELinux, or equivalent controls.
• Monitor kernel logs for crashes, KASAN reports, warnings, or oops traces involving AF_XDP, xsk_skb_metadata(), checksum processing, or skb checksum helpers.
• Because EPSS is very low and there is no KEV listing or known ransomware use, handle as timely hardening rather than emergency internet-facing remediation unless the environment exposes AF_XDP to untrusted local users.
• Include this vulnerability in local privilege escalation and kernel attack-surface threat models, especially for hosts where initial application compromise could be chained into host-level impact.