CVE-2015-0833 in Firefox
Summary
by MITRE
Multiple untrusted search path vulnerabilities in updater.exe in Mozilla Firefox before 36.0, Firefox ESR 31.x before 31.5, and Thunderbird before 31.5 on Windows, when the Maintenance Service is not used, allow local users to gain privileges via a Trojan horse DLL in (1) the current working directory or (2) a temporary directory, as demonstrated by bcrypt.dll.
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Analysis
by VulDB Data Team • 05/17/2022
The vulnerability identified as CVE-2015-0833 represents a critical privilege escalation issue affecting Mozilla Firefox and Thunderbird installations on Windows systems. This flaw exists within the updater.exe component that handles software updates for these applications. The vulnerability stems from improper handling of dynamic link library (DLL) loading mechanisms when the Maintenance Service is not actively employed during the update process. Attackers can exploit this weakness by placing malicious DLL files in specific locations that the updater.exe process will search through during execution, thereby enabling unauthorized privilege escalation.
The technical exploitation occurs through untrusted search path vulnerabilities that allow attackers to manipulate the DLL loading sequence. When Firefox or Thunderbird attempts to update without the Maintenance Service, the updater.exe process searches for required libraries in predictable locations including the current working directory and temporary directories. The vulnerability specifically demonstrates the risk through the use of bcrypt.dll as a Trojan horse example, where an attacker places a malicious version of this legitimate system DLL in a directory that gets searched before the system's legitimate DLL location. This behavior violates the principle of least privilege and creates a path for local attackers to execute code with elevated privileges. The flaw operates under CWE-427 Uncontrolled Search Path Element, which specifically addresses situations where applications search for libraries in untrusted directories, and aligns with ATT&CK technique T1068 for local privilege escalation through DLL hijacking.
The operational impact of this vulnerability is significant for organizations deploying Firefox or Thunderbird on Windows platforms. Local users who can write to the affected directories can execute arbitrary code with the privileges of the affected application, potentially leading to complete system compromise. The vulnerability affects multiple versions including Firefox 36.0 and earlier, Firefox ESR 31.x versions prior to 31.5, and Thunderbird versions before 31.5, representing a substantial user base that requires immediate attention. The risk is particularly elevated in environments where users have local account access but should not possess administrative privileges, as this creates a direct path for privilege escalation attacks.
Mitigation strategies for CVE-2015-0833 focus primarily on updating to patched versions of the affected software, which Mozilla released as part of Firefox 36.0, Thunderbird 31.5, and Firefox ESR 31.5. Organizations should ensure that the Maintenance Service is properly configured and enabled for automatic updates, as this service provides a more secure update mechanism that avoids the vulnerable search path behavior. Additionally, system administrators should implement proper directory permissions and monitoring to prevent unauthorized DLL placement in critical directories. The remediation approach aligns with security best practices outlined in NIST SP 800-128 and follows the principle of defense in depth by combining software patching with operational security measures. Regular vulnerability assessments and penetration testing should verify that the update process has been properly implemented and that no legacy installations remain vulnerable to this specific exploitation vector.