The Linux kernel vulnerability CVE-2025-40183 involves a memory leak in the bpf_redirect_neigh() helper function used in BPF egress gateway implementations such as Cilium's. Specifically, when forwarding packets via vxlan tunnels in collect metadata mode, the kernel allocates metadata_dst objects attached to skb buffers. However, bpf_redirect_neigh() replaces the skb's destination entry without freeing the existing metadata_dst, causing a persistent memory leak in the kernel's kmalloc-256 slab cache. This issue was resolved by fixing the handling of the metadata_dst object to ensure proper release before setting a new destination entry.

The vulnerability leads to a kernel memory leak that can cause resource exhaustion over time, potentially resulting in denial of service due to kernel memory depletion. There is no direct confidentiality or integrity impact reported. The issue affects systems using the BPF egress gateway feature with vxlan tunnels, such as Kubernetes clusters using Cilium for network traffic management.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, users should monitor kernel memory usage on affected systems and consider disabling or limiting the use of the BPF egress gateway feature with vxlan tunnels if feasible. Follow updates from the Linux kernel maintainers and Cilium project for patches addressing this issue.