The security threat concerns a vulnerability identified as CVE-2024-4367 affecting Firefox Extended Support Release (ESR) version 115.11, specifically within the PDF.js component. PDF.js is a JavaScript-based PDF renderer integrated into Firefox to display PDF documents natively within the browser. The vulnerability allows arbitrary JavaScript execution through crafted PDF files, enabling an attacker to execute malicious scripts when a user opens a malicious PDF in the vulnerable Firefox ESR version. The exploit leverages the way PDF.js processes certain PDF objects, particularly font matrices and shading patterns, to inject and execute JavaScript code. The provided exploit code is written in Python 3 and generates a malicious PDF file embedding the payload. When this PDF is opened in Firefox ESR 115.11, the arbitrary JavaScript executes within the browser context, potentially leading to unauthorized actions such as data theft, session hijacking, or further exploitation of the host system. The exploit does not require user authentication but does require user interaction in the form of opening the malicious PDF. The vulnerability is remote and can be exploited over the internet by delivering the malicious PDF via email, web downloads, or other file-sharing methods. No official patch links are provided yet, and no known exploits in the wild have been reported at the time of publication. The exploit code is publicly available, increasing the risk of widespread exploitation once weaponized. The vulnerability impacts confidentiality, integrity, and potentially availability depending on the payload executed. Given that Firefox ESR is widely used in enterprise and governmental environments for its stability and extended support, this vulnerability poses a significant risk to organizations relying on this browser version for secure document handling.

European organizations using Firefox ESR 115.11 are at risk of arbitrary JavaScript execution when opening malicious PDFs, which can lead to data breaches, credential theft, and lateral movement within networks. The ability to execute JavaScript remotely can facilitate drive-by downloads, installation of malware, or exploitation of other browser or system vulnerabilities. This is particularly critical for sectors handling sensitive information such as finance, healthcare, government, and critical infrastructure. The exploit could undermine trust in document handling processes and lead to regulatory non-compliance under GDPR if personal data is compromised. Additionally, the attack vector via PDF files is common and user interaction is often unavoidable, increasing the likelihood of successful exploitation. The lack of a patch and the availability of exploit code heighten the urgency for mitigation. Organizations may face operational disruptions and reputational damage if exploited. The threat also complicates remote work environments where PDF documents are frequently exchanged and viewed.

1. Immediate deployment of Firefox ESR versions later than 115.11 once patches are released by Mozilla. Monitor Mozilla security advisories closely for updates. 2. Implement strict email filtering and attachment scanning to detect and quarantine suspicious PDF files, especially those originating from untrusted sources. 3. Disable or restrict PDF.js usage in Firefox ESR via enterprise policies or configure Firefox to open PDFs externally in a dedicated PDF reader that is not vulnerable. 4. Educate users on the risks of opening unsolicited or unexpected PDF attachments and encourage verification of document sources. 5. Employ endpoint detection and response (EDR) solutions capable of detecting anomalous JavaScript execution within browsers. 6. Use sandboxing or virtualization for opening PDF files in isolated environments to prevent lateral movement or system compromise. 7. Regularly audit and update browser configurations and extensions to minimize attack surface. 8. Consider network-level controls to block or monitor PDF file downloads from untrusted or unknown sources. 9. Maintain comprehensive backups and incident response plans to quickly recover from potential breaches.