CVE-2026-74480
Description
A flaw was found in the Linux kernel's network bridge module. When handling multicast fast-leave, a vulnerability exists where the system may attempt to access a port group after it has been deleted. This can occur if multicast-to-unicast was previously enabled and then disabled, leading to a stale pointer. This memory corruption vulnerability could lead to system instability or a denial of service.
Statement
If the multicast-to-unicast feature has not been explicitly enabled on any bridge port (it is disabled by default), the vulnerable code path cannot be reached. Systems that do not use Linux bridge interfaces - for example, systems that are not acting as hypervisors, container hosts, or network gateways - are not affected by this flaw.
Mitigation
If bridge multicast snooping is not required, it can be disabled to prevent the vulnerable code path from being reached:
echo 0 > /sys/class/net/<bridge>/bridge/multicast_snoopingThe br_multicast_leave_group() code path is only reachable when multicast snooping is active, so disabling it eliminates exposure to this flaw.
Alternatively, avoid toggling multicast_to_unicast on bridge ports after it has been enabled. If multicast snooping is required, ensure that multicast_to_unicast is either left at its default (disabled) or, once enabled on a port, is not subsequently disabled while the port has active multicast group memberships.
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 | 7.8 | N/A | 9.8 |
| Attack Vector | Local | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | Low | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory
If the expired pointer is used in a read operation, an attacker might be able to control data read in by the application.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If the expired pointer references a memory location that is not accessible to the product, or points to a location that is "malformed" (such as NULL) or larger than expected by a read or write operation, then a crash may occur.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If the expired pointer is used in a function call, or points to unexpected data in a write operation, then code execution may be possible.
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