Xen Security Advisory CVE-2026-23555 / XSA-481
version 2
Xenstored DoS by unprivileged domain
Any guest issuing a Xenstore command accessing a node using the
(illegal) node path "/local/domain/", will crash xenstored due to a
clobbered error indicator in xenstored when verifying the node path.
Note that the crash is forced via a failing assert() statement in
xenstored. In case xenstored is being built with NDEBUG #defined,
an unprivileged guest trying to access the node path "/local/domain/"
will result in it no longer being serviced by xenstored, other guests
(including dom0) will still be serviced, but xenstored will use up
all cpu time it can get.
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.
In case xenstored has been built with NDEBUG defined, an unprivileged
domain can force xenstored to be 100% busy, but without harming
xenstored functionality for other guests otherwise.
Signed-off-by: Fernando Rodrigues <alpha@sigmasquadron.net>
Xen Security Advisory CVE-2026-23554 / XSA-480
version 3
Use after free of paging structures in EPT
The Intel EPT paging code uses an optimization to defer flushing of any cached
EPT state until the p2m lock is dropped, so that multiple modifications done
under the same locked region only issue a single flush.
Freeing of paging structures however is not deferred until the flushing is
done, and can result in freed pages transiently being present in cached state.
Such stale entries can point to memory ranges not owned by the guest, thus
allowing access to unintended memory regions.
Privilege escalation, Denial of Service (DoS) affecting the entire host,
and information leaks are possible impacts of this vulnerability.
Signed-off-by: Fernando Rodrigues <alpha@sigmasquadron.net>
Sandro