CVE-2003-0791 in Mozilla
Summary
by MITRE
The Script.prototype.freeze/thaw functionality in Mozilla 1.4 and earlier allows attackers to execute native methods by modifying the string used as input to the script.thaw JavaScript function, which is then deserialized and executed.
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Analysis
by VulDB Data Team • 06/29/2021
The vulnerability identified as CVE-2003-0791 represents a critical security flaw in Mozilla 1.4 and earlier versions that specifically targets the JavaScript engine's handling of script serialization and deserialization processes. This vulnerability resides within the Script.prototype.freeze and Script.prototype.thaw methods, which are designed to serialize and restore JavaScript script objects respectively. The flaw occurs when attackers manipulate the string input passed to the script.thaw function, enabling them to inject and execute arbitrary native code within the browser environment.
The technical exploitation of this vulnerability leverages the inherent deserialization mechanism that occurs when the thaw function processes input strings. When a malicious user provides crafted input to the script.thaw function, the JavaScript engine attempts to deserialize the provided data structure, which inadvertently triggers execution of native methods that should remain isolated from user-controlled input. This represents a classic buffer overflow and code execution vulnerability, where the boundary between safe script execution and native code manipulation becomes compromised. The vulnerability is particularly dangerous because it operates at the JavaScript engine level, allowing attackers to bypass traditional browser security boundaries and execute arbitrary code with the privileges of the running browser process.
From an operational impact perspective, this vulnerability creates significant risk for users of older Mozilla browser versions, as it enables remote code execution attacks that can compromise entire user systems. Attackers can craft malicious web pages that, when loaded in vulnerable browsers, automatically execute harmful code without user interaction. The vulnerability affects not just individual users but also organizations that may still be using outdated browser versions, creating widespread exposure across legacy systems. This type of vulnerability aligns with CWE-121, which describes heap-based buffer overflow conditions, and demonstrates the dangers of improper input validation in serialization frameworks. The attack surface is particularly broad since it can be exploited through web-based attacks, making it a prime target for phishing campaigns and drive-by downloads.
Security mitigations for this vulnerability primarily involve immediate browser updates to versions that have patched the serialization flaw, as well as implementing network-level protections such as web application firewalls that can detect and block malicious script thaw operations. Organizations should also consider implementing strict browser security policies that disable or restrict JavaScript functionality in environments where the risk is high. The remediation process requires careful attention to ensure that all instances of the vulnerable Mozilla versions are updated, as partial updates or continued use of older versions can leave systems exposed to exploitation. This vulnerability underscores the importance of keeping software current and demonstrates how seemingly benign serialization features can become attack vectors when proper input validation and sandboxing mechanisms are inadequate. The incident also highlights the need for robust code review processes that examine the interaction between high-level scripting languages and underlying native code execution environments, as defined by ATT&CK technique T1059.007 for JavaScript and related scripting languages.