CVE-2015-2743 in Firefox
Summary
by MITRE
PDF.js in Mozilla Firefox before 39.0 and Firefox ESR 31.x before 31.8 and 38.x before 38.1 enables excessive privileges for internal Workers, which might allow remote attackers to execute arbitrary code by leveraging a Same Origin Policy bypass.
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Analysis
by VulDB Data Team • 10/22/2024
The vulnerability identified as CVE-2015-2743 represents a critical privilege escalation flaw within Mozilla Firefox's PDF.js implementation that affected versions prior to 39.0 and specific ESR releases. This vulnerability resides in the browser's handling of internal worker processes responsible for rendering PDF documents, creating a dangerous vector for remote code execution attacks. The flaw specifically exploits how Firefox manages security boundaries between different execution contexts, particularly when processing PDF content through its embedded JavaScript engine.
The technical root cause of this vulnerability stems from improper privilege management within Firefox's PDF.js subsystem where internal worker threads are granted excessive permissions beyond their intended scope. This over-privilege allocation creates a scenario where malicious PDF documents can manipulate these workers to perform actions that should be restricted to the browser's core security domains. The vulnerability specifically enables attackers to bypass the Same Origin Policy, a fundamental web security mechanism that normally prevents scripts from one origin from accessing resources of another origin. This bypass allows the malicious code to execute with elevated privileges that would normally be restricted.
The operational impact of CVE-2015-2743 is severe and far-reaching, as it provides remote attackers with a pathway to execute arbitrary code on affected systems without user interaction. An attacker could craft a malicious PDF document that, when opened in an affected Firefox version, would trigger the vulnerable worker processes and execute malicious payloads with the privileges of the browser itself. This vulnerability affects not only individual users but also enterprise environments where Firefox is widely deployed, potentially allowing attackers to establish persistent access, exfiltrate sensitive data, or deploy additional malware. The exploitability is particularly concerning because PDF documents are commonly encountered in email attachments and web downloads, making this a highly practical attack vector.
This vulnerability aligns with CWE-276, which addresses improper privileges, and maps to ATT&CK technique T1059.007 for JavaScript execution and T1070.004 for bypassing security controls. The flaw demonstrates a classic case of privilege escalation through improper access control mechanisms, where the security boundary between different execution contexts is improperly enforced. Organizations should prioritize immediate patching of affected Firefox versions, implementing network-level controls to block suspicious PDF content, and monitoring for indicators of compromise related to PDF-based attacks. Additionally, browser hardening measures such as disabling PDF rendering in web browsers or implementing content security policies can provide additional defense-in-depth layers against exploitation attempts. The vulnerability underscores the importance of maintaining up-to-date browser security patches and implementing comprehensive vulnerability management processes to protect against similar privilege escalation flaws in web browser components.