Adobe has released emergency updates to fix a critical security flaw in Acrobat Reader that has come under active exploitation in the wild.
The vulnerability, assigned the CVE identifier CVE-2026-34621, carries a CVSS score of 8.6 out of 10.0. Successful exploitation of the flaw could allow an attacker to run malicious code on affected installations.
It has been described as a case of prototype pollution that could result in arbitrary code execution. Prototype pollution refers to a JavaScript security vulnerability that permits an attacker to manipulate an application's objects and properties.
The issue impacts the following products and versions for both Windows and macOS -
- Acrobat DC versions 26.001.21367 and earlier (Fixed in 26.001.21411)
- Acrobat Reader DC versions 26.001.21367 and earlier (Fixed in 26.001.21411)
- Acrobat 2024 versions 24.001.30356 and earlier (Fixed in 24.001.30362 for Windows and 24.001.30360 for macOS)
Adobe acknowledged that it's "aware of CVE-2026-34621 being exploited in the wild."
The development comes days after security researcher and EXPMON founder Haifei Li disclosed details of zero-day exploitation of the flaw to run malicious JavaScript code when opening specially crafted PDF documents through Adobe Reader. There is evidence suggesting that the vulnerability may have been under exploitation since December 2025.
"It appears that Adobe has determined the bug can lead to arbitrary code execution — not just an information leak," EXPMON said in a post on X. "This aligns with our findings and those of other security researchers over the last few days."
Update
The U.S. Cybersecurity and Infrastructure Security Agency (CISA), on April 13, 2026, added CVE-2026-34621 to its Known Exploited Vulnerabilities (KEV) catalog, requiring Federal Civilian Executive Branch (FCEB) agencies to apply the fixes by April 27, 2026.
(The story was updated after publication to reflect the change in CVSS score from 9.6 to 8.6. In a revision to its advisory on April 12, 2026, Adobe said it adjusted the attack vector from Network (AV:N) to Local (AV:L).)
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