CVE-2024-20721 is a medium-severity vulnerability affecting Adobe Acrobat Reader integrated within Microsoft Edge (version 120.0.2210.91 and earlier). The root cause is improper input validation (CWE-20), which allows an unauthenticated attacker to trigger an application denial-of-service (DoS) condition. Specifically, the vulnerability can be exploited when a user opens a maliciously crafted PDF file in Acrobat Reader for Edge. The flaw does not impact confidentiality or integrity but results in a loss of availability by crashing or otherwise disrupting the application. Exploitation requires user interaction, as the victim must open the malicious file, and no prior authentication or elevated privileges are needed. The CVSS 3.1 base score is 5.5, reflecting the local attack vector (AV:L), low attack complexity (AC:L), no privileges required (PR:N), user interaction required (UI:R), unchanged scope (S:U), and impact limited to availability (A:H). No known exploits are currently reported in the wild, and no patches have been linked yet. This vulnerability highlights the importance of robust input validation in PDF rendering components embedded in browsers, as malformed inputs can lead to application crashes and service disruption.

For European organizations, this vulnerability primarily threatens the availability of Adobe Acrobat Reader within Microsoft Edge, potentially disrupting workflows that rely on PDF document viewing and processing. Sectors with heavy dependence on PDF documents—such as legal, finance, government, and education—may experience operational interruptions if users open malicious PDFs. Although the impact is limited to denial-of-service and does not compromise data confidentiality or integrity, repeated or targeted exploitation could degrade user productivity and cause temporary loss of access to critical documents. Since exploitation requires user interaction, phishing or social engineering campaigns could be used to deliver malicious PDFs. The lack of known exploits in the wild reduces immediate risk, but organizations should remain vigilant given the widespread use of Adobe Acrobat Reader in Edge. The vulnerability could also be leveraged as part of a multi-stage attack to cause disruption or distract security teams.

European organizations should implement the following specific mitigations: 1) Educate users to be cautious when opening PDF attachments or links from untrusted or unexpected sources, emphasizing the risk of denial-of-service via malicious PDFs. 2) Restrict or monitor the use of Acrobat Reader within Edge where possible, especially in high-risk user groups, and consider alternative PDF viewers with a better security track record. 3) Deploy endpoint protection solutions capable of detecting anomalous application crashes or suspicious PDF files. 4) Apply application whitelisting and sandboxing techniques to limit the impact of crashes and prevent lateral movement. 5) Monitor Adobe and Microsoft security advisories closely for patches or updates addressing this vulnerability and prioritize timely deployment once available. 6) Implement email filtering and attachment scanning to block or quarantine suspicious PDF files before reaching end users. 7) Consider disabling or limiting the use of Acrobat Reader integration in Edge if not essential, or configure Edge to use a different PDF handler.