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CVE-2026-23557: Xenstored DoS via XS_RESET_WATCHES command

• Severity: medium (CVSS 6.5 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: 2026-05-19 · updated 2026-10-14
• Weakness: CWE-617

Description

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.

Affected products

• xen: from 4.2.0

References

• https://xenbits.xenproject.org/xsa/advisory-484.html
• http://www.openwall.com/lists/oss-security/2026/04/28/11
• http://xenbits.xen.org/xsa/advisory-484.html

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