CVE-2020-27874 in WeChat
Summary
by MITRE • 02/11/2021
This vulnerability allows remote attackers to execute arbitrary code on affected installations of Tencent WeChat 7.0.18. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file. The specific flaw exists within the WXAM Decoder. The issue results from the lack of proper validation of user-supplied data, which can result in a memory access past the end of an allocated object. An attacker can leverage this vulnerability to execute code in the context of the current process. Was ZDI-CAN-11580.
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Analysis
by VulDB Data Team • 02/27/2021
The vulnerability identified as CVE-2020-27874 represents a critical memory corruption flaw within Tencent WeChat version 7.0.18 that exposes users to remote code execution risks. This security weakness resides in the WXAM Decoder component, which is responsible for processing specific data formats within the messaging application. The vulnerability manifests when the application fails to properly validate user-supplied data during the decoding process, creating opportunities for malicious actors to manipulate memory structures. This particular flaw falls under the CWE-125 vulnerability category, which specifically addresses out-of-bounds read conditions that can lead to unpredictable behavior and potential code execution. The attack vector requires user interaction through visiting malicious web pages or opening compromised files, making it particularly dangerous in social engineering scenarios where users might be tricked into engaging with malicious content.
The technical implementation of this vulnerability stems from improper bounds checking within the WXAM Decoder module, where the application does not adequately verify the size or content of incoming data streams before processing them. When legitimate data structures are processed, the decoder attempts to access memory locations beyond the allocated buffer boundaries, creating a condition where arbitrary memory can be read or modified. This memory corruption scenario allows attackers to manipulate the application's execution flow and potentially inject malicious code into the running process. The vulnerability operates at the application layer and leverages the principle of memory safety violations that are commonly exploited in modern exploit development frameworks. Attackers can craft specially designed malicious files or web content that, when processed by WeChat, triggers the out-of-bounds memory access, ultimately leading to privilege escalation and code execution within the application's security context.
The operational impact of this vulnerability extends beyond simple data corruption, as it provides attackers with a pathway to establish persistent access to user devices through the WeChat application. This represents a significant concern for enterprise security environments where WeChat is commonly used for business communications, as it could enable attackers to access sensitive corporate data or use the compromised device as a foothold for further network penetration. The vulnerability's exploitation requires user interaction, which aligns with ATT&CK technique T1203 - Exploitation for Client Execution, where adversaries leverage application vulnerabilities to execute malicious code. Organizations may face increased risk of data breaches, credential theft, and unauthorized access to personal information stored within WeChat's ecosystem. The memory corruption nature of the flaw means that even if the initial exploit fails, subsequent attempts may result in application crashes or more severe system instability.
Mitigation strategies for CVE-2020-27874 should prioritize immediate patch deployment from Tencent, as the vulnerability affects a widely used messaging application with significant user adoption. Security administrators should implement network-based controls to monitor and block suspicious content that might trigger the vulnerable decoder, including filtering for known malicious file signatures and implementing web application firewalls. User education programs should emphasize the importance of avoiding untrusted links and attachments, particularly those that might trigger automatic downloads or processing within WeChat. Organizations should also consider implementing endpoint detection and response solutions that can identify anomalous behavior patterns consistent with memory corruption exploits. The vulnerability highlights the importance of secure coding practices and proper input validation, as recommended by industry standards such as the OWASP Secure Coding Practices and NIST guidelines for memory safety in application development. Regular security assessments and vulnerability scanning should include checks for similar out-of-bounds access conditions in other third-party applications that might be similarly susceptible to exploitation.