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CVE-2026-34621

High CVSS 8.6 Known exploited

Published 2026-04-11 · last changed 2026-08-28 · added to CISA KEV 2026-04-13

This one is being exploited in the wild.

CISA added CVE-2026-34621 to the Known Exploited Vulnerabilities catalog on 2026-04-13. Federal agencies are required to remediate it on a deadline. If you have affected machines, this is the class of finding that moves ahead of the rest of the queue.

The fix

We hold no Microsoft remediation data for CVE-2026-34621, which normally means it is not a Windows CVE. For non-Microsoft software the fix is the vendor's own updated release, and the affected versions are listed below.

What it is

Acrobat Reader versions 24.001.30356, 26.001.21367 and earlier are affected by an Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') vulnerability that could result in arbitrary code execution in the context of the current user. Exploitation of this issue requires user interaction in that a victim must open a malicious file.

Sources

CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H