CVE-2021-27431
📋 TL;DR
This vulnerability in ARM CMSIS RTOS2 allows integer wrap-around in memory allocation functions, potentially leading to arbitrary memory allocation. This could cause system crashes or allow attackers to execute injected code. It affects systems using ARM CMSIS RTOS2 versions prior to 2.1.3.
💻 Affected Systems
- ARM CMSIS RTOS2
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data exfiltration, or persistent backdoor installation.
Likely Case
System crashes or denial of service due to memory corruption, potentially leading to device instability.
If Mitigated
Limited impact with proper memory protection mechanisms and exploit mitigations in place.
🎯 Exploit Status
Exploitation requires understanding of memory allocation patterns and system architecture.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.1.3
Vendor Advisory: https://developer.arm.com/documentation/ka005185/latest/
Restart Required: Yes
Instructions:
1. Download ARM CMSIS RTOS2 version 2.1.3 or later from ARM developer portal. 2. Replace vulnerable library files with patched versions. 3. Recompile affected applications. 4. Deploy updated firmware to affected devices. 5. Restart devices to apply changes.
🔧 Temporary Workarounds
Memory allocation bounds checking
allImplement additional bounds checking in memory allocation routines to prevent integer wrap-around.
// Custom wrapper for osRtxMemoryAlloc with size validation
void* safe_alloc(size_t size) {
if (size > MAX_ALLOWED_SIZE) return NULL;
return osRtxMemoryAlloc(size);
}
🧯 If You Can't Patch
- Implement network segmentation to isolate vulnerable devices from critical systems.
- Enable memory protection features like MPU (Memory Protection Unit) if available on the hardware.
🔍 How to Verify
Check if Vulnerable:
Check CMSIS RTOS2 library version in project configuration files or by examining compiled binaries for version strings.Check Version:
grep -r "CMSIS_RTOS2_VERSION" project_files/ || strings binary_file | grep "CMSIS"Verify Fix Applied:
Verify that CMSIS RTOS2 version is 2.1.3 or later in project configuration and compiled binaries.📡 Detection & Monitoring
Log Indicators:
- Unexpected system crashes or reboots
- Memory allocation failures in system logs
- Abnormal memory usage patterns
Network Indicators:
- Unusual network traffic from embedded devices
- Unexpected outbound connections from IoT devices
SIEM Query:
source="device_logs" AND ("crash" OR "reboot" OR "memory allocation failed")