CVE-2026-23557 | Xenstored DoS via XS_RESET_WATCHES command

Any guest can cause xenstored to crash by issuing a XS_RESET_WATCHES command within a transaction due to an assert() triggering. In case xenstored was built with NDEBUG #defined nothing bad will happen, as assert() is doing nothing in this case. Note that the default is not to define NDEBUG for xenstored builds even in release builds of Xen.

Published: 2026-05-19 Last update: 2026-05-19 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-23557 is rated Low Risk (28/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.16%). 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-2026-23557

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 2026-06-15 0.01% 0.16% +0.15%
2 2026-05-20 — 0.01% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-23557

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/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:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.0 4.0 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2026-23557

GitHub Security Advisory for CVE-2026-23557

GHSA-9879-vj7m-r497 · Severity: medium — Any guest can cause xenstored to crash by issuing a XS_RESET_WATCHES command within a transaction...

OS Trackers for CVE-2026-23557

vendor priority summary link
debian unimportant CVE-2026-23557 unimportant priority: Debian including 1 source packages (xen), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 5. https://security-tracker.debian.org/tracker/CVE-2026-23557
suse medium CVE-2026-23557 severity moderate: SUSE including 40 source package names (xen, xen-4.12.4_66-3.140.1, …), 67 product×package rows across 16 product lines (SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS, SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS, … (16 product lines)): First Fixed 33, Fixed 33, Known Not Affected 1. https://www.suse.com/security/cve/CVE-2026-23557/
ubuntu medium CVE-2026-23557 medium priority: Ubuntu including 1 source packages (xen), 8 status rows across 8 suites (bionic, focal, jammy, noble, questing, resolute, upstream, xenial): needs-triage 8. https://ubuntu.com/security/CVE-2026-23557

Affected software / configurations for CVE-2026-23557

Vendor Product Version Raw CPE
xen xen >= 4.2.0 cpe:2.3:o:xen:xen:*:*:*:*:*:*:*:*

References for CVE-2026-23557

cvelogic Threat Intelligence