CVE-2018-5158 in Siebel Industry-Life Sciences
Summary
by MITRE
The PDF viewer does not sufficiently sanitize PostScript calculator functions, allowing malicious JavaScript to be injected through a crafted PDF file. This JavaScript can then be run with the permissions of the PDF viewer by its worker. This vulnerability affects Firefox ESR < 52.8 and Firefox < 60.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability described in CVE-2018-5158 represents a critical security flaw in the PDF viewer component of Mozilla Firefox browsers. This issue specifically targets the handling of PostScript calculator functions within PDF documents, creating a pathway for arbitrary JavaScript code execution. The flaw exists in the sanitization process that should prevent potentially harmful code from being processed by the PDF rendering engine. When a malicious PDF file is opened, the viewer fails to properly validate or sanitize the PostScript calculator functions, allowing attacker-controlled JavaScript to be embedded within the document structure.
The technical implementation of this vulnerability stems from insufficient input validation within the PDF parsing logic. PostScript calculator functions are used within PDF documents to perform mathematical operations and can contain embedded code that gets executed during document rendering. The PDF viewer's worker process, which operates with elevated privileges to handle document processing, becomes vulnerable when these functions are not properly sanitized. This creates an environment where malicious actors can craft PDF files containing carefully constructed calculator functions that, when processed by the viewer, execute arbitrary JavaScript code with the permissions of the PDF viewer itself. The vulnerability affects both Firefox Extended Support Release versions prior to 52.8 and regular Firefox versions before 60, indicating it was present across multiple browser channels for an extended period.
The operational impact of this vulnerability extends beyond simple code execution, as it allows attackers to leverage the PDF viewer's elevated permissions to perform actions that would normally be restricted. When JavaScript code executes within the PDF worker process, it can access system resources, manipulate document content, or potentially exfiltrate data from the user's system. The worker process context provides significant privileges that can be abused to compromise the user's environment, making this vulnerability particularly dangerous in targeted attacks. Security researchers have classified this issue under CWE-20, which represents "Improper Input Validation," and it aligns with ATT&CK technique T1203, "Exploitation for Client Execution," as it exploits the PDF viewer to execute malicious code on the target system.
Organizations and users affected by this vulnerability should immediately implement mitigations to protect against exploitation. The primary recommendation involves updating to the patched versions of Firefox browsers, specifically Firefox ESR 52.8 and Firefox 60 or later, which contain the necessary sanitization fixes for PostScript calculator functions. Additionally, administrators should consider implementing PDF scanning solutions that can detect and block malicious PDF files before they reach end users. Network-level controls such as web application firewalls or content filtering systems can also help mitigate the risk by blocking suspicious PDF content or implementing strict validation policies for document handling. Security teams should also conduct regular vulnerability assessments to ensure that all Firefox installations are properly patched and that users are educated about the risks of opening untrusted PDF files from unknown sources.