CVE-2005-2702 in Firefox
Summary
by MITRE
Firefox before 1.0.7 and Mozilla Suite before 1.7.12 allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via Unicode sequences with "zero-width non-joiner" characters.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 06/10/2019
The vulnerability described in CVE-2005-2702 represents a critical security flaw affecting Mozilla Firefox versions prior to 1.0.7 and the Mozilla Suite versions before 1.7.12. This issue stems from improper handling of Unicode sequences containing zero-width non-joiner characters, which are invisible Unicode characters used in typography to prevent ligatures between letters. The flaw manifests when these specific Unicode sequences are processed by the affected browsers, leading to unpredictable behavior that can result in system crashes or potentially allow remote code execution.
The technical root cause of this vulnerability lies in the browser's Unicode processing engine failing to properly validate and sanitize input containing zero-width non-joiner characters. These characters, while invisible to users, can be embedded within web content and scripts in ways that trigger buffer overflows or memory corruption within the browser's rendering engine. When the browser attempts to process these malformed Unicode sequences, the parsing logic becomes unstable, causing the application to crash or potentially allowing attackers to inject malicious code that executes with the privileges of the browser process.
From an operational perspective, this vulnerability presents significant risks to users of affected browser versions. Attackers can craft malicious web pages containing carefully constructed Unicode sequences that exploit this flaw when viewed in vulnerable browsers. The potential for remote code execution makes this particularly dangerous as it could allow attackers to gain unauthorized access to systems, install malware, or perform other malicious activities. The zero-width nature of these characters makes detection difficult as they are invisible to users and can be easily embedded within legitimate web content without raising suspicion.
The impact of this vulnerability extends beyond simple denial of service as it represents a potential path to full system compromise. According to CWE classification, this vulnerability maps to CWE-129, which deals with insufficient validation of length or count of input data, and CWE-787, which addresses out-of-bounds write conditions. The ATT&CK framework categorizes this under T1059 for command and scripting interpreter and T1203 for exploitation for privilege escalation. Organizations using affected browser versions face substantial risk of targeted attacks, particularly in environments where users may encounter untrusted web content.
Mitigation strategies for this vulnerability require immediate patching of affected browser installations to the recommended versions that contain proper Unicode validation mechanisms. System administrators should implement browser lockdown policies and consider deploying web application firewalls to filter suspicious Unicode content. Additionally, users should be educated about the risks of visiting untrusted websites and the importance of keeping browser software updated. The vulnerability highlights the critical importance of proper input validation in web browsers and underscores the need for comprehensive Unicode handling in security-critical applications. Organizations should also consider implementing network-based intrusion detection systems that can identify and block attempts to exploit this specific vulnerability pattern.