CVE-2020-28895: VxWorks Buffer Overflow Vulnerability

CVE-2020-28895 Overview

In Wind River VxWorks, the memory allocator has a possible overflow in calculating the memory block's size to be allocated by calloc(). As a result, the actual memory allocated is smaller than the buffer size specified by the arguments, leading to memory corruption. This integer overflow vulnerability affects the VxWorks real-time operating system (RTOS), which is widely deployed in embedded systems, industrial control systems, aerospace, and telecommunications infrastructure.

Critical Impact

Integer overflow in the calloc() function can result in undersized memory allocations, enabling attackers to trigger memory corruption that may lead to arbitrary code execution, denial of service, or information disclosure on affected VxWorks-based systems.

Affected Products

• Wind River VxWorks (versions prior to security patches)
• Wind River VxWorks 6.9.4.12
• Oracle Communications EAGLE (versions 46.6.0 to 46.7.0 and 46.8.0 to 46.9.2)

Discovery Timeline

• 2021-02-03 - CVE CVE-2020-28895 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-28895

Vulnerability Analysis

The vulnerability resides in the VxWorks memory allocator, specifically within the calloc() function implementation. The calloc() function is designed to allocate memory for an array of elements, taking two parameters: the number of elements and the size of each element. It multiplies these values to determine the total memory required.

When the multiplication of these two parameters exceeds the maximum representable value for the data type used in the calculation, an integer overflow occurs. This causes the result to wrap around to a smaller value than intended. Consequently, the memory allocator provisions a buffer significantly smaller than what the calling code expects.

When the application subsequently writes data to this undersized buffer assuming the originally requested size, it writes beyond the allocated memory boundaries. This memory corruption can overwrite adjacent heap metadata or other critical data structures.

Root Cause

The root cause is an integer overflow vulnerability (CWE-190) in the size calculation performed by the calloc() function. The implementation fails to properly validate that the multiplication of the element count and element size does not exceed the maximum value representable by the size type. Without this bounds check, attackers can craft inputs that trigger the overflow condition, resulting in a much smaller allocation than intended by the caller.

Attack Vector

The vulnerability can be exploited remotely over a network connection. An attacker who can influence the parameters passed to calloc() through network-accessible interfaces can trigger the integer overflow condition. The attack requires no authentication or user interaction.

The exploitation scenario involves:

1. Identifying network services on VxWorks-based devices that process attacker-controlled data
2. Crafting malicious input that causes calloc() to be called with large values for both the element count and size parameters
3. The multiplication of these values overflows, resulting in a small allocation
4. Subsequent operations write beyond the undersized buffer, corrupting heap memory
5. The attacker leverages the memory corruption to achieve code execution or denial of service

Given VxWorks' prevalence in critical infrastructure such as industrial control systems, medical devices, and telecommunications equipment, successful exploitation could have significant real-world impact.

Detection Methods for CVE-2020-28895

Indicators of Compromise

• Unexpected system crashes or reboots on VxWorks-based devices, particularly during network operations
• Memory corruption errors or heap corruption detected in system logs
• Abnormal network traffic patterns targeting VxWorks services with unusually large parameter values
• Process termination or undefined behavior following memory allocation operations

Detection Strategies

• Monitor network traffic for anomalous requests containing large numeric values that could trigger integer overflows
• Implement integrity monitoring on VxWorks-based embedded systems to detect unexpected modifications
• Deploy network intrusion detection signatures to identify exploitation attempts targeting VxWorks devices
• Review application logs for memory allocation failures or corruption indicators

Monitoring Recommendations

• Establish baseline behavior for VxWorks-based devices and alert on deviations
• Monitor for unusual restart patterns or crash loops on affected embedded systems
• Implement network segmentation to isolate VxWorks devices and enable focused monitoring
• Configure centralized logging for VxWorks devices where possible to correlate potential attack indicators

How to Mitigate CVE-2020-28895

Immediate Actions Required

• Apply vendor-provided patches from Wind River immediately for all affected VxWorks deployments
• For Oracle Communications EAGLE deployments, apply the patches referenced in the April 2022 Critical Patch Update
• Isolate vulnerable VxWorks-based systems behind network firewalls to reduce attack surface
• Implement network access controls to restrict which hosts can communicate with VxWorks devices
• Conduct inventory assessment to identify all VxWorks-based systems in your environment

Patch Information

Wind River has released security patches to address this vulnerability. Detailed patch information is available through the Wind River CVE Advisory and the Wind River Defect Report V7LIBC-1327. Organizations using Oracle Communications EAGLE should reference the Oracle Critical Patch Update April 2022 for applicable patches.

Workarounds

• Implement network segmentation to isolate VxWorks devices from untrusted networks
• Deploy application-layer firewalls or proxies to filter requests with suspiciously large parameter values
• Disable or restrict access to unnecessary network services on affected VxWorks systems
• Where possible, implement input validation at the application layer before calling memory allocation functions

# Network segmentation example - restrict access to VxWorks devices
# Example iptables rules to limit access to VxWorks device subnet
iptables -A FORWARD -d 10.0.100.0/24 -s 10.0.1.0/24 -j ACCEPT
iptables -A FORWARD -d 10.0.100.0/24 -j DROP