CVE-2025-10263: Arm Processor Privilege Escalation Flaw

CVE-2025-10263 Overview

CVE-2025-10263 affects a broad range of Arm CPU designs, including Cortex-A, Cortex-X, and Neoverse families. The flaw permits writes to resources owned by a higher exception level, breaking the architectural privilege boundary that isolates hypervisors and secure monitors from lower-privileged code. The issue is tracked under CWE-362 as a race condition. Arm published technical details in ARM Documentation Release 112137, and the Xen Project issued Advisory XSA-493 addressing hypervisor exposure.

Critical Impact
A lower-privileged execution context can modify resources owned by a higher exception level, undermining hypervisor and guest isolation on widely deployed Arm cores.

Affected Products

Arm Cortex-A76 & A76A, Cortex-A77, Cortex-A78/A78AE/A78C, Cortex-A710
Arm Cortex-X1 & X1C, Cortex-X2, Cortex-X3, Cortex-X4, Cortex-X925
Arm Neoverse-N1, Neoverse-N2, Neoverse V1, Neoverse V2, Neoverse V3 & V3AE, C1-Premium, C1-Ultra

Discovery Timeline

2026-06-09 - CVE-2025-10263 published to the National Vulnerability Database
2026-06-09 - Xen Project Advisory XSA-493 released
2026-06-09 - Last updated in NVD database

Technical Details for CVE-2025-10263

Vulnerability Analysis

The vulnerability is a race condition [CWE-362] in the microarchitecture of multiple Arm Cortex-A, Cortex-X, and Neoverse CPU designs. Under specific concurrent execution sequences, a lower-privileged context can issue writes that land on resources architecturally owned by a higher exception level. Exception levels on Armv8/v9 separate user code (EL0), kernel (EL1), hypervisor (EL2), and secure monitor (EL3). Crossing that boundary through writes violates the core security model used by virtualization and confidential computing on Arm. Cloud providers and Xen-based deployments are directly exposed, as confirmed by the Xen Project advisory.

Root Cause

The root cause is a timing window in how affected cores arbitrate access to privileged system registers and memory-mapped resources. Concurrent operations from different exception levels can interleave in a way that allows a write originating from a lower exception level to commit against state that should be reserved for a higher one. Arm classifies this as a microarchitectural defect in the listed CPU implementations rather than a software flaw in any single operating system.

Attack Vector

Exploitation requires the attacker to execute code at a lower exception level on an affected core, such as a guest kernel running under a hypervisor. By orchestrating concurrent accesses that align with the vulnerable timing window, the attacker can corrupt or overwrite hypervisor-owned state. In multi-tenant cloud environments, this can be used to escape guest isolation, tamper with hypervisor data structures, or alter resources controlled by EL2. No verified public exploit is available at this time, and the EPSS probability remains low.

No verified public proof-of-concept code is available. Refer to ARM Documentation Release 112137 and the Openwall OSS-Security disclosure for architectural detail.

Detection Methods for CVE-2025-10263

Indicators of Compromise

Unexpected modification of hypervisor-owned system registers or control structures on Arm hosts running affected cores.
Guest VMs exhibiting anomalous access patterns to system registers immediately before hypervisor instability or crashes.
Hypervisor logs reporting integrity faults, unexpected EL2 state transitions, or panics on Cortex-A/X or Neoverse hardware.

Detection Strategies

Inventory Arm-based hosts and identify systems running the listed Cortex-A, Cortex-X, and Neoverse cores using lscpu, dmidecode, or cloud provider instance metadata.
Correlate hypervisor crash dumps and guest exit reasons with the affected CPU implementations to surface suspicious EL1-to-EL2 interactions.
Apply the Xen Project mitigations documented in XSA-493 and monitor for advisory bypass attempts in audit logs.

Monitoring Recommendations

Enable verbose hypervisor logging on Xen and other Arm hypervisors to capture abnormal exception level transitions.
Forward host kernel, hypervisor, and cloud control plane logs to a central analytics platform for correlation with the affected CPU inventory.
Track vendor firmware and microcode advisories tied to the affected Arm cores and alert on hosts that fall behind on patches.

How to Mitigate CVE-2025-10263

Immediate Actions Required

Identify all systems running the affected Arm Cortex-A, Cortex-X, and Neoverse cores, including bare-metal servers, cloud instances, and edge devices.
Apply the Xen Project updates described in XSA-493 to all Xen hypervisors running on affected hardware.
Coordinate with cloud and silicon vendors to obtain firmware, microcode, or hypervisor updates referenced in ARM Documentation Release 112137.

Patch Information

Arm published architectural guidance and mitigation requirements in ARM Documentation Release 112137. The Xen Project released XSA-493 with patches for affected Xen versions. Operating system and cloud vendors are expected to ship corresponding hypervisor and kernel updates; consult vendor advisories for the specific build numbers applicable to each platform.

Workarounds

Where patches are not yet available, restrict workloads on affected cores to single-tenant use to remove the cross-guest threat model.
Disable or constrain nested virtualization on affected Arm hosts until vendor updates are deployed.
Pin sensitive workloads to host classes whose CPUs are not in the affected list when offered by the cloud provider.

bash

# Identify Arm CPU implementer and part to determine exposure
lscpu | grep -E 'Model name|Vendor ID|CPU implementer|CPU part'
cat /proc/cpuinfo | grep -E 'CPU implementer|CPU part|CPU variant'

# On Xen hosts, verify the running hypervisor version against XSA-493
xl info | grep -E 'xen_version|xen_commandline'