Xen ships batch of fixes for guest escapes spanning grant tables, pygrub, and more

Xen Project has published a batch of security advisories closing multiple guest-to-host privilege escalation paths and related flaws that stretch across years of hypervisor releases.

The sharpest cluster sits in grant tables. XSA-500 (CVE-2026-62428) is a type confusion in grant-copy handling: when a grant is already pinned by another operation, permission checks and the actual copy can land on different pages. An unprivileged guest may raise its privileges to the host; information leaks and denial of service are also possible. Xen 4.2 and later are affected unless grant-table support was built out. Roman S. discovered the bug.

XSA-501 covers two races when guests switch grant-table versions (CVE-2026-62435 for v1-to-v2, CVE-2026-62436 for v2-to-v1). Code that drops and reacquires the grant-table lock can assume properties that change underfoot, again enabling host privilege escalation, leaks, or DoS. Only multi-vCPU x86 guests allowed to use grant-table v2 can exploit it; Xen 4.0 and later are vulnerable. Limiting grants to version 1 via hypervisor or guest config avoids the issue. Mark Esler reported it.

Five buffer overruns in libfsimage iso9660 handling land under XSA-497 (CVE-2026-42494, CVE-2026-42495, CVE-2026-62423, CVE-2026-62424, CVE-2026-62425). Directory and Rock Ridge walks take lengths straight from on-disk fields without enough validation. A guest using pygrub can escalate to the domain construction tools and normally to host control. Running pygrub de-privileged, dropping pygrub, or using only HVM or PVH guests mitigates the risk. Syed Abdul Khaliq of BugQore found the flaws. Versions from at least 3.2 are affected.

XSA-502 (CVE-2026-62429) fixes a race during vNUMA domain cleanup. Device models can still read vNUMA configuration after destruction has started. Denial of service and information leaks are the common outcome; a stub-domain or de-privileged device model may also reach host privileges. Only HVM guests with vNUMA enabled expose the path. Teddy Astie of Vates discovered it. Xen 4.5 and later are vulnerable.

XSA-507 (CVE-2026-62434) stops populate-on-demand guests from reclaiming special pages, which corrupted Xen memory-management state on x86 HVM and PVH guests since 3.4. Crashes and other malfunctions follow; information leak and privilege escalation cannot be ruled out. Avoiding PoD or running only PV guests sidesteps it.

XSA-505 (CVE-2026-62432) closes a race between FIFO event-channel array expansion and reset that can dereference a null pointer and crash the hypervisor. Malicious HVM guests on x86 or Arm can cause denial of service; for x86 PV guests, memory corruption or privilege escalation cannot be ruled out. No mitigations are listed. Xen 4.5 and later are affected.

Patches are available for the relevant stable branches. Operators should update promptly.