CVE-2007-3917 in Wesnoth
Summary
by MITRE
The multiplayer engine in Wesnoth 1.2.x before 1.2.7 and 1.3.x before 1.3.9 allows remote servers to cause a denial of service (crash) via a long message with multibyte characters that can produce an invalid UTF-8 string after it is truncated, which triggers an uncaught exception, involving the truncate_message function in server/server.cpp. NOTE: this issue affects both clients and servers.
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Analysis
by VulDB Data Team • 07/29/2021
The vulnerability identified as CVE-2007-3917 represents a critical denial of service weakness in the multiplayer networking infrastructure of the popular turn-based strategy game Wesnoth. This flaw affects versions 1.2.x prior to 1.2.7 and 1.3.x prior to 1.3.9, creating a scenario where remote adversaries can exploit the game's communication protocols to crash both client and server instances. The vulnerability specifically targets the truncate_message function located within server/server.cpp, which handles message processing in the multiplayer environment. The issue stems from inadequate validation of multibyte character sequences during message truncation operations, creating a condition where properly formatted UTF-8 data can become corrupted when subjected to the truncation process. This flaw operates at the intersection of network protocol handling and string manipulation, making it particularly dangerous in multiplayer gaming environments where continuous communication between participants is essential for game operation.
The technical execution of this vulnerability relies on the manipulation of UTF-8 encoded multibyte characters within network messages. When a malicious actor sends a specially crafted message containing long sequences of multibyte characters, the truncate_message function processes this data by cutting it off at predetermined length limits. However, the truncation algorithm does not properly account for UTF-8 encoding boundaries, which can result in the creation of invalid UTF-8 sequences when the message is shortened. This occurs because multibyte UTF-8 characters consist of multiple bytes where each byte has specific bit patterns that must remain intact for valid encoding. When truncation cuts off a character in the middle of its byte sequence, it creates malformed UTF-8 data that cannot be properly interpreted by subsequent processing functions. The resulting invalid UTF-8 string triggers an uncaught exception within the application's error handling mechanism, leading to immediate program termination and system crash. This type of vulnerability falls under CWE-129, which addresses improper validation of length parameters, and specifically relates to CWE-704, concerning incorrect type conversion or cast operations. The vulnerability's impact extends beyond simple service disruption to potentially compromise the entire multiplayer gaming session.
The operational consequences of CVE-2007-3917 are severe for both individual players and game administrators who manage multiplayer servers. When exploited, this vulnerability can cause immediate crashes of both client applications and server instances, effectively disrupting gameplay for all connected participants. The denial of service condition affects the availability of the multiplayer feature entirely, as the game becomes unusable until the affected process is manually restarted. This vulnerability is particularly concerning in public gaming environments or competitive multiplayer settings where server stability is crucial for maintaining fair play conditions and user experience. The attack vector requires only network access to a Wesnoth server, making it extremely accessible to potential attackers and capable of being exploited at scale. In the context of the ATT&CK framework, this vulnerability maps to T1499.004, which covers "Utilities: Endpoint Denial of Service," and represents a classic case of resource exhaustion through malformed input processing. The impact extends to both client and server components, meaning that even individual players could be affected if they connect to a compromised server, creating a broader attack surface than typical server-side vulnerabilities. The vulnerability demonstrates how seemingly innocuous character encoding operations can create critical security weaknesses when proper boundary checking and validation are not implemented.
Mitigation strategies for CVE-2007-3917 require immediate implementation of proper UTF-8 validation and boundary checking within the message truncation process. The most effective approach involves modifying the truncate_message function in server/server.cpp to validate UTF-8 encoding integrity before and after truncation operations, ensuring that no partial multibyte sequences are created. System administrators should implement network-level filtering to limit message sizes and monitor for unusual character patterns that might indicate exploitation attempts. The recommended fix involves implementing proper UTF-8 validation routines that check for valid character boundaries before truncation and potentially implementing a maximum message length enforcement mechanism. Additionally, the application should be updated to version 1.2.7 or 1.3.9, where the vulnerability has been patched. Organizations managing Wesnoth servers should also consider implementing intrusion detection systems that can identify and block malformed network traffic patterns associated with this vulnerability. The vulnerability highlights the importance of proper input validation in networked applications and serves as a reminder that character encoding issues can create critical security weaknesses. Regular security updates and code reviews focusing on string handling and network protocol implementations should be prioritized to prevent similar issues from emerging in other software components. This vulnerability demonstrates that even fundamental operations like message truncation require careful attention to encoding standards and boundary conditions to maintain application stability and security.