CVE-2026-34621

Adobe Acrobat and Acrobat Reader are affected by a prototype pollution vulnerability (CWE-1321) in which improperly controlled modification of object prototype attributes can lead to arbitrary code execution in the context of the current user. Attackers trigger the flaw by convincing a victim to open a malicious file, typically a crafted PDF, so user interaction is required. Successful exploitation yields code execution as the victim, with the CVSS scope-changed metric indicating impact that extends beyond the vulnerable component. Anyone running Acrobat or Reader versions 24.001.30356 or earlier or 26.001.21367 or earlier is affected. The flaw is being actively exploited in the wild — reportedly via malicious PDFs since December 2025 as a zero-day — and CISA added it to the Known Exploited Vulnerabilities catalog on 2026-04-13 after fixes shipped in Adobe's April 2026 Patch Tuesday release; EPSS assigns a 7.1% probability of exploitation within 30 days (94th percentile).

What to do: Upgrade Acrobat and Reader to a version later than 24.001.30356 (24.001 series) or 26.001.21367 (26.001 series) via Adobe's April 2026 security update, and audit installed versions across all endpoints. As a CISA KEV entry, US federal agencies must apply the vendor mitigations per BOD 22-01 guidance or discontinue use of the product if mitigations are unavailable. Until patched, treat PDFs from untrusted sources with caution and monitor for suspicious child-process activity spawned by Acrobat/Reader when files are opened.