CVE-2026-98047 bpf: Check ancestor frames for rbtree callbacks
A local attacker can trigger a use-after-free in the Linux kernel BPF rbtree implementation via nested callbacks, potentially leading to privilege escalation or code execution.
- 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-2026-98047?
CVE-2026-98047 is an use after free vulnerability in Linux, published on 25 Sep 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:
bpf: Check ancestor frames for rbtree callbacks
bpf_rbtree_add() invokes its comparator while the caller holds the root lock. The native insertion code retains raw parent and link pointers across the callback, so the verifier prohibits unlocking, consuming tree nodes, or changing RCU state from that callback.
in_rbtree_lock_required_cb() only checks the innermost verifier frame. Static subprogram calls are permitted while holding a spin lock, and such a call pushes a frame without in_callback_fn set. Consequently, all callback restrictions disappear in the nested frame. The subprogram can unlock the tree, remove and drop the node being compared, then relock. Native insertion resumes with the stale parent pointer and links freed memory into the tree.
Walk all active frames for the rbtree callback instead. Benign static subprograms remain permitted, while callback restrictions follow execution into nested frames.
Which versions are affected by CVE-2026-98047?
How do I fix CVE-2026-98047?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-98047 being exploited?
There is no known exploitation of CVE-2026-98047 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-98047, DEBIAN-CVE-2026-98047, GHSA-4vcw-h5gp-c67p, UBUNTU-CVE-2026-98047.