CVE-2026-46086
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
A vulnerability has been identified in the Linux kernel that allows inconsistent reads of local FDB entries in bridges. The issue arises from multiple loads of the `f->dst` value, which can lead to a NULL pointer dereference.
Risk Assessment
This vulnerability may lead to system crashes or unexpected behavior of network bridges, posing a risk to the stability and security of network infrastructure.
Recommendation
It is recommended to update the Linux kernel to a version that includes a fix for this vulnerability to ensure the stability and security of bridge operations.
Original NVD description (English source)
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.