CVE-2025-40254

Open vSwitch NSH (Network Service Header) field modification has been fundamentally broken since introduction. The set(nsh(...)) action reuses validation code designed for different memory layouts—masked sets double attribute sizes, but the validator doesn't account for this. Additionally, 'masked' and 'is_mask' flags are conflated, causing SW_FLOW_KEY_PUT() to write into unallocated mask memory, triggering NULL pointer crashes.

The feature never functioned correctly, so removing it causes no regression. Any flow rules attempting NSH field modification would have failed or crashed. Networks depending on NSH header manipulation should verify they use push_nsh() rather than set().

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, prevent the openvswitch module from being loaded. See https://access.redhat.com/solutions/41278 for instructions on how to blacklist a kernel module.