CVE-2026-98591 bpf: Fix bounds check for skb-backed dynptrs
An integer underflow in Linux kernel BPF bounds checking allows attackers to access invalid memory, potentially leading to code execution or privilege escalation.
- 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-2026-98591?
CVE-2026-98591 is a vulnerability in Linux, published on 18 Oct 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: Fix bounds check for skb-backed dynptrs
The skb_pointer_if_linear() function checks whether a memory region of length len starting at offset off into the skb is in the linear area, and returns a pointer to the region if so. The check currently subtracts between skb_headlen and offset of the check, and since skb_headlen is unsigned the subtraction can underflow. This causes the bounds check to spuriously pass and generate an arbitrary pointer of the form *(skb->data + off).
The only user of this helper is currently skb-backed BPF dynptr code. Returning the wrong pointer leads to the dynptr erroneously being backed with invalid memory.
Ensure the subtraction cannot underflow, and fail the check if it would. Use u64 arithmetic to also prevent overflow when calculating (skb_headlen(skb) - off) since off is unsigned.
Which versions are affected by CVE-2026-98591?
How do I fix CVE-2026-98591?
Apply the vendor's patch.
Is CVE-2026-98591 being exploited?
There is no known exploitation of CVE-2026-98591 in the wild and no public exploit code.
Sources
Also known as AZL-109223, BELL-CVE-2026-98591, DEBIAN-CVE-2026-98591, GHSA-4j29-hvp6-5v88, UBUNTU-CVE-2026-98591.