CVE-2026-53250
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk4th percentile — higher than 4% of all known CVEs
Summary
A TOCTOU vulnerability was found in the Linux kernel's xsk_skb_metadata() function for AF_XDP sockets. The csum_start and csum_offset fields are read twice from shared UMEM memory, allowing a malicious userspace process to overwrite them between reads, bypassing bounds checks and causing out-of-bounds memory access during checksum computation in the transmit path.
Risk Assessment
An attacker with access to an AF_XDP socket can cause kernel memory corruption, potentially leading to system crash (DoS) or privilege escalation.
Recommendation
Immediately apply the Linux kernel patch that fixes the issue by reading csum_start and csum_offset into local variables once before validation and assignment.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: xsk: cache csum_start/csum_offset to fix TOCTOU in xsk_skb_metadata() The TX metadata area resides in the UMEM buffer which is memory-mapped and concurrently writable by userspace. In xsk_skb_metadata(), csum_start and csum_offset are read from shared memory for bounds validation, then read again for skb assignment. A malicious userspace application can race to overwrite these values between the two reads, bypassing the bounds check and causing out-of-bounds memory access during checksum computation in the transmit path. Fix this by reading csum_start and csum_offset into local variables once, then using the local copies for both validation and assignment. Note that other metadata fields (flags, launch_time) and the cached csum fields may be mutually inconsistent due to concurrent userspace writes, but this is benign: the only security-critical invariant is that each field's validated value is the same one used, which local caching guarantees.