CVE-2026-23557: Any guest can cause xenstored to crash by issuing a XS_RESET_WATCHES command within a transaction due to an as

Routine

MEDIUM 6.5MITIGATE

CVE-2026-23557 is a medium-severity flaw (CVSS 6.5) affecting xen. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 95%)
CISA exploited list	No
Weakness	CWE-617
Published	2026-05-19
Last modified	2026-10-14

Publisher (CNA): Xen Project · Vendor: xen

Last updated 2026-10-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-19 14:16 UTCPublished CVE record published
2026-10-14 20:10 UTCUpdated Record last modified

xen xen MITIGATE

Affected: >= 4.2.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.2.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-23557?

xen: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-23557 being exploited?

CVE-2026-23557 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-23557 affect?

CVE-2026-23557 affects xen. Severity is medium (CVSS 6.5). 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

How urgent is CVE-2026-23557?

Priority 24/100. No elevated risk signals yet.

Software pages

Xen vulnerabilities

Related CVEs

CVE-2026-23558 HIGH 7.8 MITIGATE The adjustments made for XSA-379 as well as those subsequently becoming XSA-387 still left a race window, when

References

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