CVE-2025-0647: Arm CPU Privilege Escalation Vulnerability

CVE-2025-0647 Overview

CVE-2025-0647 is a hardware-level vulnerability affecting certain Arm CPUs where a CPP RCTX (Coherent Processing Protocol Register Context) instruction executed on one Processing Element (PE) may inhibit TLB (Translation Lookaside Buffer) invalidation when a TLBI (TLB Invalidate) is issued. This flaw can cause the affected PE to retain stale TLB entries that should have been invalidated, either from instructions issued by the same PE or another PE in the shareability domain.

Critical Impact

This vulnerability can lead to information disclosure and integrity violations as stale TLB entries may allow unauthorized memory access or incorrect memory mappings, potentially enabling privilege escalation or cross-process data leakage in multi-core environments.

Affected Products

• Certain Arm CPUs with CPP RCTX instruction support
• Systems utilizing multi-processing element (PE) configurations
• Platforms with shared TLB invalidation domains

Discovery Timeline

• 2026-01-14 - CVE CVE-2025-0647 published to NVD
• 2026-01-20 - Last updated in NVD database

Technical Details for CVE-2025-0647

Vulnerability Analysis

This vulnerability (CWE-226: Sensitive Information in Resource Not Removed Before Reuse) stems from improper handling of TLB cache coherency when CPP RCTX instructions interact with TLBI operations. In multi-core Arm processors, TLB invalidation is critical for maintaining memory isolation between processes and privilege levels. When a TLBI instruction is issued, all relevant TLB entries across the shareability domain should be invalidated to ensure stale address translations are not used.

The flaw occurs because the CPP RCTX instruction, which manages register context for coherent processing protocols, can inadvertently block or delay TLB invalidation broadcasts. This race condition means that even after a TLBI is executed, some PEs may continue using outdated address translations, potentially accessing memory regions that should no longer be mapped or accessible.

Root Cause

The root cause lies in the microarchitectural interaction between the CPP RCTX instruction pipeline and the TLB invalidation broadcast mechanism. When CPP RCTX executes, it may temporarily inhibit the PE's ability to process incoming TLBI broadcasts from the interconnect or ignore locally-issued invalidations. This creates a window where stale TLB entries persist despite explicit invalidation requests, violating the expected memory management semantics.

Attack Vector

The attack vector requires local access with high privileges (such as kernel or hypervisor level) to execute the CPP RCTX instruction in a manner that triggers the vulnerability. An attacker with sufficient privileges could potentially:

1. Time CPP RCTX execution to coincide with critical TLBI operations
2. Cause stale TLB entries to persist, allowing access to memory pages that should have been unmapped
3. Exploit the stale mappings to read sensitive data from other processes or bypass memory isolation
4. In virtualized environments, potentially escape guest isolation by accessing hypervisor or other guest memory

The local attack vector and high privilege requirement somewhat limit the exploitability, but the scope change indicator suggests impact beyond the vulnerable component, making this particularly concerning for virtualization and container environments.

Detection Methods for CVE-2025-0647

Indicators of Compromise

• Unexpected memory access patterns in kernel or hypervisor logs suggesting stale TLB usage
• Anomalous cross-process or cross-VM memory access attempts
• System crashes or memory corruption errors following TLBI operations on multi-core systems

Detection Strategies

• Monitor for unusual CPP RCTX instruction usage patterns through hardware performance counters
• Implement kernel-level auditing of TLB management operations on affected Arm processors
• Deploy memory integrity verification to detect unauthorized cross-boundary memory access

Monitoring Recommendations

• Enable hardware performance monitoring for TLB-related events on affected Arm architectures
• Implement anomaly detection for memory access violations in virtualized environments
• Review system logs for segmentation faults or memory errors that may indicate TLB coherency issues

How to Mitigate CVE-2025-0647

Immediate Actions Required

• Review the Arm Documentation Resource for affected CPU models and firmware updates
• Assess your infrastructure for affected Arm processors and prioritize patching based on exposure
• Consider restricting CPP RCTX instruction usage in untrusted contexts where possible

Patch Information

Arm has published documentation regarding this vulnerability. System administrators should consult the Arm Security Advisory for specific microcode or firmware updates applicable to their hardware. Operating system and hypervisor vendors may also release kernel patches that implement software workarounds for this issue.

Workarounds

• Implement additional TLB invalidation barriers in critical code paths as a defensive measure
• Consider disabling or restricting CPP RCTX instruction usage through kernel configuration if operationally feasible
• In virtualized environments, evaluate additional memory isolation controls at the hypervisor level

# Check Arm CPU model and firmware version
cat /proc/cpuinfo | grep -E "(CPU implementer|CPU architecture|CPU variant|CPU part)"

# Review kernel messages for TLB-related warnings
dmesg | grep -i tlb

# Monitor for memory access violations
journalctl -k | grep -E "(segfault|page fault|memory)"