CVE-2026-98033 bpf: Preserve inner map identity in callback frames
A use-after-free vulnerability in the Linux kernel BPF subsystem allows local attackers to execute arbitrary code or escalate privileges via timer callbacks.
- 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-2026-98033?
CVE-2026-98033 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: Preserve inner map identity in callback frames
Callback frame constructors initialize map-typed argument registers with __mark_reg_known_zero() and then restore map_ptr. This clears map_uid, which is the only field distinguishing inner maps that share an inner_map_meta template.
When a timer callback invokes bpf_for_each_map_elem() on a second inner map, both the saved first map and the second map value can reach the nested callback as the same template with map_uid zero. bpf_timer_init() then accepts pairing the timer from the second map with the first map.
The runtime records the first map in the timer without taking a reference. Freeing that map does not find the timer stored in the second map, so a later timer callback dereferences the freed map.
Copy map_uid from the same caller register as map_ptr when constructing for-each, timer/workqueue, and task-work callback arguments. The existing identity check can then reject mismatched inner maps while allowing a callback value to be paired with its actual map.
Which versions are affected by CVE-2026-98033?
How do I fix CVE-2026-98033?
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-2026-98033 being exploited?
There is no known exploitation of CVE-2026-98033 in the wild and no public exploit code.
Sources
Also known as AZL-104549, BELL-CVE-2026-98033, DEBIAN-CVE-2026-98033, GHSA-4746-9qhc-mc6f, UBUNTU-CVE-2026-98033.