CVE-2024-44934 is a use-after-free vulnerability identified in the Linux kernel's network bridge multicast garbage collection mechanism. Specifically, the flaw occurs in the function br_multicast_port_group_expired within the net/bridge/br_multicast.c source file. The vulnerability arises because the bridge code does not ensure that all previous garbage collection (GC) cycles have completed before removing a port. In a multi-CPU environment, one CPU may initiate a GC cycle while another CPU concurrently removes a port and frees its associated memory without waiting for the GC cycle to finish. This race condition leads to a use-after-free scenario where timers related to multicast group management continue to run and access freed memory, causing kernel memory corruption. The issue was discovered by syzbot, a kernel fuzzing tool, and is evidenced by a KASAN (Kernel Address Sanitizer) report indicating a slab-use-after-free error. The root cause is that the bridge code fails to flush pending work (via flush_work) before freeing the port, allowing stale timers to execute on freed objects. This vulnerability affects Linux kernel versions prior to the fix introduced around the 6.10.0-rc5 release cycle. While no known exploits are reported in the wild yet, the nature of the flaw—kernel memory corruption due to improper synchronization—makes it a significant risk for denial of service or potential privilege escalation if exploited. The vulnerability is subtle and requires concurrent operations on bridge ports and multicast GC cycles, but it can be triggered by crafted network configurations or workloads that manipulate bridge ports and multicast groups rapidly.

For European organizations, this vulnerability poses a risk primarily to systems running Linux kernels with bridging enabled, especially in environments using multicast networking such as data centers, cloud infrastructure, and enterprise networks. The use-after-free can lead to kernel crashes (denial of service), destabilizing critical network infrastructure. In worst cases, it could be leveraged for privilege escalation or arbitrary code execution within the kernel context, threatening confidentiality and integrity of data and systems. Organizations relying on Linux-based network appliances, virtualized environments, or container orchestration platforms that use Linux bridging (e.g., Open vSwitch, Docker networking) are particularly at risk. Disruptions could affect service availability, impacting business continuity. Given the widespread use of Linux in European government, financial, telecommunications, and industrial sectors, the vulnerability could have broad operational impacts if exploited. Although no active exploits are known, the vulnerability’s presence in kernel code that handles network bridging—a critical function in many enterprise networks—means attackers with local or network access could attempt to trigger the flaw. This elevates the threat level for organizations with exposed Linux systems or multi-tenant environments where untrusted users have some level of access.

European organizations should prioritize patching Linux kernels to versions that include the fix for CVE-2024-44934 as soon as updates are available from their Linux distribution vendors. Until patches are applied, administrators should: 1) Minimize use of Linux bridge multicast features if not required, or disable multicast snooping and related bridge features to reduce attack surface. 2) Restrict access to systems running Linux bridges, ensuring only trusted users and processes can manipulate bridge ports or multicast groups. 3) Monitor kernel logs and use kernel debugging tools to detect signs of use-after-free or KASAN reports indicative of exploitation attempts. 4) Employ network segmentation to isolate critical Linux bridge hosts from untrusted networks or users. 5) For virtualized or container environments, ensure hypervisor and container runtimes are updated and consider additional isolation controls to limit impact of kernel vulnerabilities. 6) Engage with Linux distribution security advisories and subscribe to vulnerability notifications to respond rapidly to new information or exploit reports. 7) Conduct internal testing of patches in staging environments to validate stability before deployment in production.