CVE-2025-21156 is an integer underflow vulnerability classified under CWE-191 affecting Adobe InCopy versions 20.0, 19.5.1, and earlier. An integer underflow occurs when an arithmetic operation attempts to create a numeric value smaller than the minimum representable value, causing wraparound behavior that can lead to memory corruption. In this case, the vulnerability can be triggered by opening a maliciously crafted InCopy file, which causes the application to mishandle internal data structures due to the underflow. This memory corruption can be leveraged by an attacker to execute arbitrary code within the context of the current user. The CVSS v3.1 base score is 7.8, indicating high severity, with attack vector local (requiring user interaction), low attack complexity, no privileges required, and user interaction necessary. The impact includes full compromise of confidentiality, integrity, and availability of the affected system. Although no exploits are currently known in the wild, the vulnerability poses a significant risk due to the widespread use of Adobe InCopy in publishing and creative industries. The lack of available patches at the time of publication necessitates immediate risk mitigation strategies.

The potential impact of CVE-2025-21156 is substantial for organizations relying on Adobe InCopy for content creation and publishing. Successful exploitation can lead to arbitrary code execution, allowing attackers to install malware, steal sensitive data, or disrupt operations. Since the code executes with the current user's privileges, the impact depends on the user's access level; administrative users could face full system compromise. The requirement for user interaction limits remote exploitation but does not eliminate risk, especially in environments where users frequently open files from external or untrusted sources. The vulnerability threatens confidentiality by enabling data theft, integrity by allowing unauthorized modifications, and availability by potentially causing application or system crashes. Industries such as media, publishing, advertising, and any enterprise using Adobe InCopy are at risk, potentially affecting business continuity and reputation.

1. Apply official patches from Adobe immediately once they become available to address the integer underflow vulnerability. 2. Until patches are released, implement strict file handling policies: restrict users from opening InCopy files from untrusted or unknown sources. 3. Employ application whitelisting and sandboxing techniques to limit the execution scope of Adobe InCopy and contain potential exploitation. 4. Educate users about the risks of opening unsolicited or suspicious files and encourage verification of file origins. 5. Monitor systems for unusual behavior or signs of exploitation, such as unexpected process activity or crashes related to Adobe InCopy. 6. Use endpoint detection and response (EDR) tools to detect and block exploitation attempts. 7. Consider network segmentation to isolate systems running Adobe InCopy from critical infrastructure to reduce lateral movement in case of compromise. 8. Regularly back up important data to enable recovery if an attack occurs.