Hackers Exploiting PDF24 App to Deploy Stealthy PDFSIDER Backdoor

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January 19, 2026 at 12:17 PM

Actively Exploited

Overview

Researchers from Resecurity have uncovered a new malware called PDFSIDER that takes advantage of the legitimate PDF24 application to steal sensitive data and provide attackers with remote access to compromised systems. This malware is part of a sophisticated campaign targeting corporate networks, utilizing spear-phishing tactics to lure victims and encrypted communications to evade detection. Companies using PDF24 should be particularly vigilant as this attack leverages a trusted application, making it easier for attackers to bypass security measures. The implications are serious, as this could lead to significant data breaches and unauthorized access to sensitive corporate information.

Key Takeaways

Active Exploitation: This vulnerability is being actively exploited by attackers. Immediate action is recommended.
Affected Systems: PDF24 App, corporate networks
Action Required: Users should monitor for unusual activity in their networks, implement strong email filtering to block spear-phishing attempts, and ensure that all software, including PDF24, is kept up to date with the latest security patches.
Timeline: Newly disclosed

Original Article Summary

Resecurity has identified PDFSIDER malware that exploits the legitimate PDF24 App to covertly steal data and allow remote access. Learn how this APT-level campaign targets corporate networks through spear-phishing and encrypted communications.

Impact

PDF24 App, corporate networks

Exploitation Status

This vulnerability is confirmed to be actively exploited by attackers in real-world attacks. Organizations should prioritize patching or implementing workarounds immediately.

Timeline

Newly disclosed

Remediation

Users should monitor for unusual activity in their networks, implement strong email filtering to block spear-phishing attempts, and ensure that all software, including PDF24, is kept up to date with the latest security patches.

Additional Information

This threat intelligence is aggregated from trusted cybersecurity sources. For the most up-to-date information, technical details, and official vendor guidance, please refer to the original article linked below.

Related Topics: This incident relates to Phishing, APT, Malware.

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