Adobe fixes a zero-day PDF security flaw that hackers have been exploiting for months

Adobe has identified a vulnerability in its document reading software, Acrobat DC, Reader DC and Acrobat 2024, which hackers have been exploiting for four months.

Vulnerability, legal enforcement if CVE-2026-34621allows hackers to plant malware on a person’s device by tricking them into opening a maliciously crafted PDF file on their Windows device or MacOS computer. Effectively combats a vulnerability in some versions of the Adobe Reader software.

It is not known how many people have been affected by the operation. In a post on its website, Adobe said it was aware of the virus being used in the wild, known as day zeroshowing that hackers have been using it to break into people’s computers before Adobe fixed it.

While it is unclear who is behind the hacking campaign, the availability of Adobe’s PDF reader software makes it possible. fixed target to cybercriminals and government-sponsored hackers who have long exploited the software’s vulnerabilities to steal data from people’s computers.

Security researcher Haifei Li, who runs the EXPMON detection system, discovered one vulnerability after another. he held up the copy of a malicious PDF that has access to its own malware. In blog postLi wrote that another PDF copy containing the malware first appeared on VirusTotal, another malware tracker, in late November 2025.

It’s unclear who the hacker is targeting or for what purpose, and Li said it was impossible to get additional information from the hacker’s servers. But according to Li’s analysis, opening a malicious PDF and launching an exploit “can lead to complete control of the victim’s system” and give the hacker an opportunity to steal more information.

Adobe said Acrobat DC, Reader DC, and Acrobat 2024 are affected, and encouraged users to update their software to the latest version.