Adobe Reader Zero-Day Exploited via Malicious PDFs Since December 2025

Threat actors have been exploiting a previously unknown zero-day vulnerability in Adobe Reader using maliciously crafted PDF documents since at least December 2025. The finding, detailed by EXPMON's Haifei Li, has been described as a highly-sophisticated PDF exploit. The artifact ("Invoice540.pdf") first appeared on the VirusTotal platform on November 28, 2025.