CVE-2026-98061 bpf: Reject tail calls directly from callback frames

Not scored Published 25 Sep 2026 Updated 19 Oct 2026

A local attacker with CAP_BPF privileges can trigger a kernel warning and denial of service by loading a BPF program that performs tail calls from callback frames.

Exploited in the wild: Not known
Login needed: An administrator
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-98061?

CVE-2026-98061 is a denial of service 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: Reject tail calls directly from callback frames

A tail call from a non-zero frame is modeled as a return from that frame. The verifier makes R0 unknown and calls prepare_func_exit() for the taken branch.

When the current frame is a synchronous callback, prepare_func_exit() enforces the callback return-value contract and marks R0 precise. Since the tail-call path synthesized R0 rather than deriving it from an instruction, precision backtracking reaches the callback-calling instruction with R0 still requested and triggers the "callback unexpected regs" verifier bug. A CAP_BPF task can therefore cause a WARN and an -EFAULT BPF_PROG_LOAD.

Tail calls reachable from callbacks are already rejected later by check_max_stack_depth(). Reject a tail call made directly by a callback before constructing the inconsistent return state, using the existing diagnostic. Tail calls from ordinary subprograms keep their current behavior.

Which versions are affected by CVE-2026-98061?

How do I fix CVE-2026-98061?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-98061 being exploited?

There is no known exploitation of CVE-2026-98061 in the wild and no public exploit code.

Sources

Also known as DEBIAN-CVE-2026-98061, GHSA-3q38-vxgf-8598, UBUNTU-CVE-2026-98061.