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

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

Published: 2026-04-30 Last update: 2026-05-06 Assigner: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-31786 is rated Low Risk (31.7/100): CVSS High severity, with low exploitation likelihood (EPSS 0.01%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-31786

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-03 0.08% 0.01% -0.07%
2 2026-04-30 — 0.08% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-31786

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.8 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 5.9 416baaa9-dc9f-4396-8d5f-8c081fb06d67

Weakness enumeration for CVE-2026-31786

GitHub Security Advisory for CVE-2026-31786

GHSA-7p99-gmjx-2f7r · Severity: high — In the Linux kernel, the following vulnerability has been resolved: Buffer overflow in drivers...

OS Trackers for CVE-2026-31786

vendor priority summary link
debian not yet assigned CVE-2026-31786 not yet assigned priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6. https://security-tracker.debian.org/tracker/CVE-2026-31786
redhat high — https://access.redhat.com/security/cve/CVE-2026-31786
suse medium CVE-2026-31786 severity moderate: SUSE including 14 source package names (cluster-md-kmp-default, dlm-kmp-default, …), 45 product×package rows across 9 product lines (SUSE Linux Enterprise Live Patching 12 SP5, SUSE Linux Enterprise Micro 5.0, … (9 product lines)): Known Not Affected 45. https://www.suse.com/security/cve/CVE-2026-31786/
ubuntu medium CVE-2026-31786 medium priority: Ubuntu including 161 source packages (linux, linux-allwinner-5.19, …), 1449 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): DNE 1067, needs-triage 209, ignored 173. https://ubuntu.com/security/CVE-2026-31786

Affected software / configurations for CVE-2026-31786

Vendor Product Version Raw CPE
linux linux_kernel >= 4.13, < 5.10.254 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.11, < 5.15.204 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.16, < 6.1.170 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.2, < 6.6.137 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.7, < 6.12.85 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.13, < 6.18.26 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.19, < 7.0.3 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel 7.1 cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:*
linux linux_kernel 7.1 cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:*

References for CVE-2026-31786

URL Tags
https://git.kernel.org/stable/c/27fdbab4221b375de54bf91919798d88520c6e28 Patch
https://git.kernel.org/stable/c/4b4defd2fce3f966c25adabf46644a85558f1169 Patch
https://git.kernel.org/stable/c/52cecff98bda2c51eed1c6ce9d21c5d6268fb19d Patch
https://git.kernel.org/stable/c/5c5ff7c7bd15bb536f44b10b3fb5b8408f344d0a Patch
https://git.kernel.org/stable/c/8288d031a01dbacfde3fc643f7be3d23504de64d Patch
https://git.kernel.org/stable/c/d5f59216650c51e5e3fcb7517c825bc8047f60ef Patch
https://git.kernel.org/stable/c/e3af585e1728c917682b6a3de9a69b41fb9194d4 Patch
https://git.kernel.org/stable/c/f458ba102da97fafca106327086fc95f3fc764cb Patch
http://www.openwall.com/lists/oss-security/2026/04/28/12 Mailing List Third Party Advisory
http://xenbits.xen.org/xsa/advisory-485.html Mailing List Third Party Advisory
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