CVE-2026-31786 Buffer overflow in drivers/xen/sys-hypervisor.c
A buffer overflow in the Linux kernel Xen driver allows attackers to execute arbitrary code or cause a denial of service via crafted hypervisor version data.
- 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-2026-31786?
CVE-2026-31786 is a high-severity memory corruption vulnerability in Linux kernel, published on 30 Apr 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:
Buffer overflow in drivers/xen/sys-hypervisor.c
The build id returned by HYPERVISOR_xen_version(XENVER_build_id) is neither NUL terminated nor a string.
The first causes a buffer overflow as sprintf in buildid_show will read and copy till it finds a NUL.
00000000 f4 91 51 f4 dd 38 9e 9d 65 47 52 eb 10 71 db 50 |..Q..8..eGR..q.P| 00000010 b9 a8 01 42 6f 2e 32 |...Bo.2| 00000017
So use a memcpy instead of sprintf to have the correct value:
00000000 f4 91 51 f4 dd 00 9e 9d 65 47 52 eb 10 71 db 50 |..Q.....eGR..q.P| 00000010 b9 a8 01 42 |...B| 00000014
(the above have a hack to embed a zero inside and check it's returned correctly).
This is XSA-485 / CVE-2026-31786
Which versions are affected by CVE-2026-31786?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31786?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-31786 being exploited?
There is no known exploitation of CVE-2026-31786 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31786, DEBIAN-CVE-2026-31786, GHSA-7p99-gmjx-2f7r, ROOT-OS-DEBIAN-11-CVE-2026-31786, ROOT-OS-UBUNTU-2204-CVE-2026-31786, UBUNTU-CVE-2026-31786.