CVE-2012-4207 in Firefox
Summary
by MITRE
The HZ-GB-2312 character-set implementation in Mozilla Firefox before 17.0, Firefox ESR 10.x before 10.0.11, Thunderbird before 17.0, Thunderbird ESR 10.x before 10.0.11, and SeaMonkey before 2.14 does not properly handle a ~ (tilde) character in proximity to a chunk delimiter, which allows remote attackers to conduct cross-site scripting (XSS) attacks via a crafted document.
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Analysis
by VulDB Data Team • 04/22/2025
The vulnerability identified as CVE-2012-4207 represents a critical cross-site scripting flaw within the character encoding handling mechanisms of several Mozilla-based applications including Firefox, Thunderbird, and SeaMonkey. This weakness specifically manifests in the HZ-GB-2312 character set implementation, which is used for processing Chinese text encoding. The flaw occurs when a tilde character is positioned near a chunk delimiter within the encoding process, creating a condition that can be exploited by malicious actors to inject arbitrary JavaScript code into web pages.
The technical root cause of this vulnerability lies in the improper parsing and handling of the HZ-GB-2312 encoding scheme, which employs a unique method for representing Chinese characters using a combination of ASCII characters and escape sequences. When the browser encounters a tilde character in proximity to a chunk delimiter during the processing of encoded content, the parser fails to properly sanitize or validate the input, allowing malicious payloads to bypass security controls. This behavior aligns with CWE-79, which describes cross-site scripting vulnerabilities that occur when untrusted data is improperly handled by web applications. The vulnerability specifically targets the character encoding layer rather than the application logic, making it particularly insidious as it can be exploited through seemingly benign content that gets processed through the affected encoding mechanism.
The operational impact of this vulnerability extends beyond simple XSS attacks, as it provides attackers with the ability to execute arbitrary code within the context of a user's browser session. This can result in session hijacking, data theft, redirection to malicious sites, or the execution of unauthorized commands on behalf of the victim. The vulnerability affects multiple widely-used applications, amplifying its potential impact across different user bases and threat scenarios. Attackers can craft malicious documents or web pages containing specifically formatted HZ-GB-2312 encoded content that triggers this flaw when processed by vulnerable browsers. The exploitability of this vulnerability is enhanced by the fact that it does not require user interaction beyond visiting a malicious page, making it particularly dangerous in phishing attacks or compromised websites.
Mitigation strategies for CVE-2012-4207 primarily involve updating affected applications to versions that contain the patched character encoding implementation. Mozilla released updates for Firefox 17.0, Thunderbird 17.0, and SeaMonkey 2.14 that address this specific vulnerability by properly handling the tilde character in proximity to chunk delimiters. Organizations should implement comprehensive patch management procedures to ensure all affected systems are updated promptly. Additionally, administrators can consider implementing content security policies that restrict script execution and monitor for unusual character encoding patterns in web traffic. From an ATT&CK framework perspective, this vulnerability maps to technique T1059.006 for script injection and T1566 for social engineering, as it can be leveraged in phishing campaigns targeting users with Chinese language content. Network-level defenses should include monitoring for suspicious encoding patterns and implementing web application firewalls that can detect and block malicious character sequences. The vulnerability also underscores the importance of proper input validation and encoding sanitization in security-critical applications, particularly those handling international character sets that may have complex encoding schemes.