CVE-2026-31786

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

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CVSS v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0001

Probability of exploitation

0.00%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-787 Out-of-bounds Write

Affected Products

Vendor	Product	Versions
linux	linux_kernel	4.13 — 5.10.254
linux	linux_kernel	5.11 — 5.15.204
linux	linux_kernel	5.16 — 6.1.170
linux	linux_kernel	6.2 — 6.6.137
linux	linux_kernel	6.7 — 6.12.85
linux	linux_kernel	6.13 — 6.18.26
linux	linux_kernel	6.19 — 7.0.3
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/27fdbab4221b375de54bf91919798d88520c6e28 https://git.kernel.org/stable/c/4b4defd2fce3f966c25adabf46644a85558f1169 https://git.kernel.org/stable/c/52cecff98bda2c51eed1c6ce9d21c5d6268fb19d https://git.kernel.org/stable/c/5c5ff7c7bd15bb536f44b10b3fb5b8408f344d0a https://git.kernel.org/stable/c/8288d031a01dbacfde3fc643f7be3d23504de64d https://git.kernel.org/stable/c/d5f59216650c51e5e3fcb7517c825bc8047f60ef https://git.kernel.org/stable/c/e3af585e1728c917682b6a3de9a69b41fb9194d4 https://git.kernel.org/stable/c/f458ba102da97fafca106327086fc95f3fc764cb

Other References

http://www.openwall.com/lists/oss-security/2026/04/28/12 http://xenbits.xen.org/xsa/advisory-485.html

Frequently Asked Questions

What is CVE-2026-31786? +

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 It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2026-31786? +

CVE-2026-31786 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0001, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-31786? +

CVE-2026-31786 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-31786? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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