CVE-2026-103937 in Misskey
Summary
by MITRE • 10/13/2026
Misskey is an open source, federated social media platform. From 13.0.0 until 2025.4.1 and from 2025.5.0 until 2026.7.0, cleanup processing may not execute during file uploads. Repeated uploads can exhaust storage or file descriptors and deny service regardless of whether federation is enabled. This issue is fixed in version 2026.7.0.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability identified within the Misskey federated social media platform represents a significant resource management failure that impacts system stability and availability across multiple software versions. Specifically, this flaw affects releases from version 13.0.0 through 2025.4.1, as well as subsequent iterations up to but not including version 2026.7.0, which includes the range from 2025.5.0 until 2026.7.0. The core technical deficiency lies in the file upload pipeline where cleanup processing is designed to remove temporary files or reset state after a transfer completes. In these affected versions, this cleanup routine fails to execute under certain conditions during file uploads. This omission means that resources allocated for handling uploaded content are not properly released back to the system pool once the operation concludes, leading to a gradual accumulation of unreleased assets on the server infrastructure.
From a technical perspective, this behavior constitutes an improper resource management issue where temporary files or open handles persist beyond their intended lifecycle. When users repeatedly upload files, whether for images, documents, or other media types, each failed cleanup event leaves behind residual data and potentially locked file descriptors. Over time, particularly in environments with high user activity or automated bot interactions, this accumulation can rapidly deplete available disk storage space. Furthermore, the operating system imposes limits on the number of open file descriptors per process; as these unreleased handles accumulate, Misskey may reach its configured limit for open files. Once this threshold is breached, the application becomes unable to accept new connections or perform further I/O operations, effectively rendering the service unresponsive to legitimate user requests.
The operational impact of this vulnerability is primarily centered on Denial of Service (DoS). An attacker can exploit this flaw by initiating a sustained series of file uploads without waiting for cleanup processes to complete naturally, thereby accelerating resource exhaustion. Notably, the severity of this issue is independent of whether federation features are enabled or disabled, meaning that even isolated instances running in standalone mode remain vulnerable. This characteristic makes it particularly dangerous as it allows local attackers with valid accounts to degrade service quality for all users on the instance. The resulting denial of service disrupts normal platform operations, preventing content creation, messaging, and feed updates until system resources are manually reclaimed or the application is restarted, which may result in data loss if not handled carefully.
In terms of industry classification standards, this vulnerability aligns closely with CWE-403: Exposure of File Descriptor to Unintended Control Sphere, as it involves the failure to properly close file descriptors after use. It also maps significantly to CWE-755: Improper Handling of Unexpected Numeric Argument if the issue stems from mishandling upload parameters that trigger the bug, and more broadly to CWE-400: Uncontrolled Resource Consumption due to the eventual exhaustion of system resources like disk space and file handles. From a tactical standpoint within the MITRE ATT&CK framework, this behavior facilitates resource hijacking for denial-of-service purposes, resembling techniques observed in DoS attacks where attackers aim to exhaust server capacity rather than compromise confidentiality or integrity directly.
Mitigation strategies must prioritize immediate software updates as the primary defense vector. Administrators operating Misskey instances should upgrade immediately to version 2026.7.0 or later, which contains the corrected cleanup logic that ensures proper resource release after file uploads complete. For environments where upgrading is not immediately feasible due to compatibility constraints or testing requirements, temporary operational mitigations include implementing strict rate limiting on upload endpoints to prevent rapid successive requests from a single source. Additionally, configuring operating system-level limits for open files and disk usage can provide a buffer against total service collapse, though these measures do not resolve the underlying application flaw. Regular monitoring of file descriptor counts and disk utilization metrics is recommended to detect early signs of resource exhaustion before they lead to full outages.