CVE-2018-5157 in Firefox
Summary
by MITRE
Same-origin protections for the PDF viewer can be bypassed, allowing a malicious site to intercept messages meant for the viewer. This could allow the site to retrieve PDF files restricted to viewing by an authenticated user on a third-party website. This vulnerability affects Firefox ESR < 52.8 and Firefox < 60.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2018-5157 represents a critical security flaw in Mozilla Firefox's handling of PDF viewer interactions within the browser's same-origin policy framework. This weakness specifically targets the isolation mechanisms that protect sensitive data processing within the browser's PDF rendering component, creating a pathway for cross-site scripting attacks that could compromise user privacy and data integrity. The vulnerability stems from insufficient enforcement of same-origin policies when the PDF viewer communicates with web content, allowing malicious actors to exploit this gap in the security model.
The technical implementation of this flaw involves the PDF viewer's message handling system failing to properly validate the origin of incoming messages, particularly when these messages are intended for the viewer's internal processing functions. Attackers can craft malicious web pages that exploit this bypass to intercept and potentially manipulate communications between the PDF viewer and legitimate web applications. This creates a scenario where authenticated sessions on third-party websites could be compromised, as the malicious site gains unauthorized access to PDF content that should remain restricted to authenticated users. The vulnerability specifically affects Firefox versions prior to 52.8 Extended Support Release and 60.0 mainline releases, indicating a prolonged window of exposure for users running affected software versions.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables sophisticated attack vectors that could lead to session hijacking, credential theft, and unauthorized access to sensitive documents. An attacker could potentially leverage this vulnerability to access PDF files containing confidential information such as financial records, personal documents, or corporate data that users expect to remain protected through authentication mechanisms. The attack surface is particularly concerning because it operates at the intersection of browser security policies and third-party content rendering, making it difficult to detect and prevent through standard security measures.
Organizations and users should prioritize immediate remediation through software updates to versions containing the patched same-origin policy enforcement for PDF viewer components. The vulnerability aligns with CWE-345 Insufficient Verification of Data Authenticity, as it involves inadequate validation of message sources within the browser's security framework. From an ATT&CK perspective, this vulnerability maps to techniques involving privilege escalation and credential access through browser-based exploitation, specifically targeting the T1056.001 technique for input validation and T1071.004 for application layer protocols. Additional mitigations include implementing strict content security policies, disabling PDF viewer functionality when unnecessary, and conducting regular security audits of web applications that interact with PDF content to ensure proper isolation mechanisms are in place.