CVE-2026-46086 net: bridge: use a stable FDB dst snapshot in RCU readers
A race condition in the Linux kernel bridge module allows a local attacker to trigger a NULL pointer dereference, causing a system crash.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-46086?
CVE-2026-46086 is a medium-severity vulnerability in Linux kernel, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-476
Which versions are affected by CVE-2026-46086?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-46086?
Apply the vendor's patch.
Is CVE-2026-46086 being exploited?
There is no known exploitation of CVE-2026-46086 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-88512, BELL-CVE-2026-46086, DEBIAN-CVE-2026-46086, GHSA-qcf5-mj4w-x99v, ROOT-OS-DEBIAN-11-CVE-2026-46086, ROOT-OS-DEBIAN-12-CVE-2026-46086 and 3 more.