CVE-2021-21099 is an out-of-bounds write vulnerability (CWE-787) found in Adobe InDesign version 16.0 and earlier. This vulnerability arises when the software parses a specially crafted InDesign file, leading to memory corruption due to writing data outside the intended buffer boundaries. Such memory corruption can be exploited by an unauthenticated attacker to execute arbitrary code remotely within the context of the current user. However, exploitation requires user interaction, specifically the victim opening a maliciously crafted InDesign file. The vulnerability does not require prior authentication, increasing its attack surface, but the need for user action limits automated exploitation. There are no known public exploits in the wild at the time of this analysis, and no official patches or updates are linked in the provided data. The vulnerability affects the confidentiality, integrity, and availability of the system by potentially allowing arbitrary code execution, which could lead to data theft, system compromise, or denial of service. Given the nature of Adobe InDesign as a professional desktop publishing application widely used in creative industries, the attack vector is primarily through social engineering or targeted spear-phishing campaigns delivering malicious InDesign files.

For European organizations, the impact of CVE-2021-21099 can be significant, especially for sectors relying heavily on Adobe InDesign for document creation, such as media, publishing, advertising, and design agencies. Successful exploitation could lead to unauthorized access to sensitive intellectual property, disruption of business operations, and potential lateral movement within corporate networks if the compromised user has elevated privileges. The confidentiality of proprietary content and client data could be at risk, and integrity of published materials could be compromised. Additionally, organizations in regulated industries may face compliance and reputational risks if breaches occur. The requirement for user interaction suggests that awareness and training are critical factors in mitigating risk. Since no known exploits are currently in the wild, the threat is more theoretical but could become practical if exploit code is developed and distributed. The medium severity rating reflects a moderate risk level but should not be underestimated given the potential for targeted attacks.

1. Immediate mitigation should focus on user education and awareness: train users to be cautious when opening InDesign files from untrusted or unknown sources, especially via email or file sharing platforms. 2. Implement strict email and file filtering policies to detect and block suspicious or unexpected InDesign files. 3. Employ endpoint protection solutions with heuristic and behavior-based detection capabilities to identify anomalous activities related to InDesign processes. 4. Restrict user privileges to the minimum necessary to reduce the impact of potential code execution. 5. Monitor for unusual process behavior or network activity originating from Adobe InDesign instances. 6. Since no official patch is linked, organizations should regularly check Adobe’s security advisories and apply updates promptly once available. 7. Consider sandboxing or isolating environments where InDesign files are opened, especially for files from external sources. 8. Maintain robust backup and incident response plans to quickly recover from potential compromises. These steps go beyond generic advice by focusing on operational controls tailored to the specific attack vector and software environment.