CVE-2023-42800 in moonlight-common-c
Summary
by MITRE • 12/14/2023
Moonlight-common-c contains the core GameStream client code shared between Moonlight clients. Moonlight-common-c is vulnerable to buffer overflow starting in commit 50c0a51b10ecc5b3415ea78c21d96d679e2288f9 due to unmitigated usage of unsafe C functions and improper bounds checking. A malicious game streaming server could exploit a buffer overflow vulnerability to crash a moonlight client, or achieve remote code execution (RCE) on the client (with insufficient exploit mitigations or if mitigations can be bypassed). The bug was addressed in commit 24750d4b748fefa03d09fcfd6d45056faca354e0.
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Analysis
by VulDB Data Team • 12/14/2023
The vulnerability identified as CVE-2023-42800 affects moonlight-common-c, a critical component that serves as the core GameStream client code shared across various Moonlight client implementations. This library forms the foundation of the streaming client architecture, making it a prime target for exploitation. The vulnerability emerged from a specific code change introduced in commit 50c0a51b10ecc5b3415ea78c21d96d679e2288f9, where developers introduced unsafe coding practices that fundamentally compromised the security posture of the client software. The issue manifests as a buffer overflow condition that can be triggered during normal client-server communication, particularly when processing data from game streaming servers.
The technical flaw stems from the improper use of unsafe C functions combined with inadequate bounds checking mechanisms within the moonlight-common-c library. This combination creates a classic buffer overflow vulnerability where malicious input data can exceed allocated memory boundaries, potentially overwriting adjacent memory locations. The vulnerability is particularly concerning because it operates at the core client level, meaning any exploitation could lead to complete client compromise. Attackers exploiting this vulnerability could cause client crashes through controlled memory corruption, or more severely achieve remote code execution on the target system. The insufficient exploit mitigations mentioned in the description indicate that the client lacks modern security protections such as stack canaries, address space layout randomization, or control flow integrity mechanisms that would otherwise prevent successful exploitation.
The operational impact of this vulnerability extends beyond simple client instability to encompass serious security risks for end users. When a malicious game streaming server is able to exploit this buffer overflow, it gains the ability to execute arbitrary code on the victim's client system, potentially leading to full system compromise. This represents a significant threat vector since game streaming clients typically run with elevated privileges and may have access to sensitive system resources. The vulnerability affects the broader Moonlight ecosystem, as multiple client implementations share this common codebase, meaning a single exploit could potentially compromise various platforms including desktop applications, mobile clients, and console implementations. The timing of the vulnerability's introduction makes it particularly dangerous, as it likely affected users who upgraded to versions containing the problematic commit, leaving them exposed without their knowledge.
The remediation for this vulnerability was addressed through commit 24750d4b748fefa03d09fcfd6d45056faca354e0, which implemented proper bounds checking and replaced unsafe C functions with safer alternatives. This fix aligns with established security best practices and represents a fundamental correction to the codebase's memory management approach. Organizations and users should prioritize updating to versions containing this fix to protect against potential exploitation. Security teams should consider implementing network monitoring to detect suspicious GameStream server activity that might indicate exploitation attempts, particularly focusing on unusual data patterns that could suggest buffer overflow attempts. The vulnerability demonstrates the importance of secure coding practices and proper code review processes, as it likely could have been prevented through better adherence to secure programming guidelines. This case study serves as a reminder of how seemingly minor code changes can introduce critical security vulnerabilities, especially in systems handling network communications with untrusted parties.
The vulnerability relates to CWE-121, which describes stack-based buffer overflow conditions, and CWE-122, which covers heap-based buffer overflow scenarios. From an ATT&CK perspective, this vulnerability maps to T1059.007 for remote code execution techniques and T1203 for exploitation of remote services. The issue also aligns with the broader category of T1595 which covers network boundary compromise through exploitation of software vulnerabilities. Organizations should ensure their security monitoring systems are configured to detect anomalous behavior patterns that might indicate exploitation attempts, particularly around memory corruption events and unexpected client crashes. The vulnerability underscores the critical need for continuous security assessment and code auditing of shared libraries, as issues in core components can propagate across entire ecosystems.