CVE-2026-53250 xsk: cache csum_start/csum_offset to fix TOCTOU in xsk_skb_metadata()
A race condition in the Linux kernel XSK module allows malicious userspace to bypass bounds checks, potentially leading to out-of-bounds memory access and code execution.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53250?
CVE-2026-53250 is a high-severity vulnerability in Linux kernel, published on 25 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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.
Weakness: CWE-367
Which versions are affected by CVE-2026-53250?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-53250?
Apply the vendor's patch.
Is CVE-2026-53250 being exploited?
There is no known exploitation of CVE-2026-53250 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-53250, DEBIAN-CVE-2026-53250, GHSA-cx83-hxfr-m85v, ROOT-OS-DEBIAN-13-CVE-2026-53250, ROOT-OS-UBUNTU-2404-CVE-2026-53250, UBUNTU-CVE-2026-53250.