CVE-2025-40254
Description
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.
Statement
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().
Mitigation
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.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 4.7 | N/A | N/A |
| Attack Vector | Local | N/A | N/A |
| Attack Complexity | High | N/A | N/A |
| Privileges Required | Low | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability,Integrity,Confidentiality
Technical Impact: Read Memory; Modify Memory; Execute Unauthorized Code or Commands; DoS: Crash, Exit, or Restart
When a memory buffer is accessed using the wrong type, it could read or write memory out of the bounds of the buffer, if the allocated buffer is smaller than the type that the code is attempting to access, leading to a crash and possibly code execution.
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