CVE-2026-23557 PUBLISHED

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.

All Xen systems from Xen 4.2 onwards are vulnerable. Systems up to Xen 4.1 are not vulnerable.

Systems using the C variant of xenstored or xenstore-stubdom built without NDEBUG are vulnerable. Systems using the OCaml variant of Xenstore (oxenstored), or the C variant (xenstored or xenstore-stubdom) built with NDEBUG defined are not vulnerable.

There is no known mitigation available.

• This issue was discovered by Andrii Sultanov of Vates. finder

• https://xenbits.xenproject.org/xsa/advisory-484.html

• Any unprivileged domain can cause xenstored to crash, causing a DoS (denial of service) for any Xenstore action. This will result in an inability to perform further domain administration on the host.