CVE-2026-74740
Description
A flaw was found in the Linux kernel's network scheduler (net/sched: act_api). A Time-of-Check to Time-of-Use (TOCTOU) race condition exists where a pointer can be cleared between two reads. This allows a concurrent operation to cause a NULL dereference, potentially leading to a system crash and Denial of Service (DoS).
Statement
A moderate-impact flaw was found in the Linux kernel's network scheduler traffic control actions API (net/sched: act_api) in the Red Hat Enterprise Linux and Red Hat In-Vehicle OS kernels. When handling a TC_ACT_GOTO_CHAIN action, tcf_action_exec() first checks the a->goto_chain pointer, and tcf_action_goto_chain_exec() then performs a second, independent read of the same pointer. A concurrent traffic control action update (for example a gact action replacement via tcf_action_set_ctrlact()) can clear a->goto_chain between the two reads, so the second read returns NULL and is dereferenced, causing a kernel panic. Exploiting this race requires local access with the privileges needed to configure traffic control actions, and the consequence is a system crash, i.e. a denial of service; confidentiality and integrity are not affected. Red Hat Enterprise Linux 7 is not affected because the vulnerable code is not present in that release. For Red Hat Enterprise Linux 6 Extended Lifecycle Support this flaw is recorded as out of support scope. The fix is deferred for the affected Red Hat Enterprise Linux and Red Hat In-Vehicle OS kernel streams; while the fix is deferred, the residual risk is limited to a denial of service caused by a local privileged attacker who is able to trigger the race.
Mitigation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
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 | 5.5 | N/A | N/A |
| Attack Vector | Local | N/A | N/A |
| Attack Complexity | Low | 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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart
NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.
Integrity,Confidentiality
Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory
In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.
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