CVE-2026-31786: Buffer overflow in drivers/xen/sys-hypervisor.c

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-30 · updated 2026-10-19
Weakness: CWE-787

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

Affected products

Linux kernel: from 4.13 before 5.10.254; from 5.11 before 5.15.204; from 5.16 before 6.1.170; from 6.2 before 6.6.137; from 6.7 before 6.12.85; from 6.13 before 6.18.26 — fixed in 5.10.254, 5.15.204, 6.1.170, 6.12.85, 6.18.26, 6.6.137

How to fix

Upgrade to a fixed version: Linux kernel 5.10.254, 5.15.204, 6.1.170, 6.12.85. Check the vendor advisory for mitigations.

References

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