CVE-2025-40183
Description
A metadata structure leak was found in the Linux kernel's BPF redirect neighbor helper functions for both IPv4 and IPv6. A local user running BPF programs can trigger this issue when redirecting packets that already have metadata_dst objects attached (such as vxlan decapsulated packets), causing the helper to overwrite the existing destination entry without releasing it first. This creates permanent memory leaks that accumulate over time, leading to resource exhaustion and denial of service.
Statement
When vxlan decapsulates packets, it attaches metadata_dst objects via fake dst entries. The bpf_redirect_neigh helper then calls skb_dst_set to attach its own dst for the redirect, but never drops the existing reference first. Each redirect leaks the vxlan metadata_dst. This manifests in Cilium's egress gateway feature where pod traffic flows through vxlan tunnels then gets BPF-redirected—kmalloc-256 slab usage grows continuously as leaked structures accumulate.
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 | 4.4 | N/A | 7.5 |
| Attack Vector | Local | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | High | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (Other)
An attacker that can influence the allocation of resources that are not properly maintained could deplete the available resource pool and prevent all other processes from accessing the same type of resource.
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