CVE-2026-16477 in CleanShot X
Summary
by MITRE • 10/22/2026
CleanShot X for macOS insecurely deserializes untrusted data embedded in a .cleanshot project file (editable screenshot annotations). Exploitation requires an attacker to craft a malicious .cleanshot file, deliver it to the target, and have the target open it; the payload then executes automatically during parsing, resulting in arbitrary code execution in the context of the current user. Users who have never opened a .cleanshot file from an untrusted source are not affected by this vulnerability. This vulnerability was fixed in versions: 4.5.2, 4.6.3, 4.7.8 and 4.8.10
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified as a critical security flaw within CleanShot X for macOS centers on the insecure deserialization of untrusted data contained in .cleanshot project files. These files are used to store editable screenshot annotations, which allows users to add notes and highlights to captured images. The core technical issue arises from the application's parsing logic, which fails to properly validate or sanitize input before processing it as serialized objects. This lack of rigorous validation enables an attacker to craft a malicious .cleanshot file that contains specially constructed data designed to exploit weaknesses in the deserialization process. When the target user opens this crafted file within CleanShot X, the application automatically parses the content without sufficient safeguards, leading directly to arbitrary code execution under the context of the currently logged-in user.
From an operational perspective, the impact of this vulnerability is severe due to its potential for remote exploitation through social engineering tactics. An attacker must first deliver a malicious .cleanshot file to the victim and persuade them to open it within CleanShot X. Once opened, the payload executes automatically during the parsing phase, granting the attacker full control over the application's runtime environment. This results in arbitrary code execution with the privileges of the current user account, which can lead to data theft, installation of additional malware, or further lateral movement within a network if the compromised machine is part of a larger infrastructure. The vulnerability specifically affects users who have opened .cleanshot files from untrusted sources; those who strictly use trusted internal files remain unaffected by this specific attack vector.
This flaw aligns with CWE-502, which describes deserialization of untrusted data as a common cause of remote code execution vulnerabilities. In the context of the MITRE ATT&CK framework, this vulnerability facilitates techniques associated with initial access and privilege escalation, particularly through file delivery mechanisms that trick users into executing malicious content. The automatic nature of the payload execution during parsing highlights a failure in implementing secure coding practices regarding object instantiation from external inputs. Such flaws are often exploited by attackers to bypass traditional security controls because they leverage legitimate application functionality for malicious purposes.
To mitigate this risk, it is imperative for organizations and individual users to update CleanShot X immediately to one of the patched versions: 4.5.2, 4.6.3, 4.7.8, or 4.8.10. These updates include fixes that enforce stricter validation on deserialized data, ensuring that only trusted and properly formatted inputs are processed by the application. Additionally, users should adopt a cautious approach when handling .cleanshot files from unknown or unverified sources, treating them with the same level of scrutiny as other potentially executable attachments. Security awareness training can further reduce the likelihood of successful exploitation by educating staff on recognizing suspicious file types and avoiding interaction with unsolicited documents until their integrity has been verified through secure channels.