CVE-2026-88016 in Rclone
Summary
by MITRE • 09/10/2026
rclone is a command-line program to sync files and directories to and from different cloud storage providers. Prior to 1.75.1, when backend/local runs with --links, a source .rclonelink object can plant a symlink in the destination and later directory metadata is applied through that path. MkdirMetadata, writeMetadataToFile, and setTimes operate when Directory.translatedLink=false, so os.Chown, os.Chmod, os.Chtimes, and birth-time handling can bypass os.Root confinement and follow the symlink. An attacker controlling source contents can therefore apply selected ownership, permissions, modification times, or birth times to a file or directory outside the destination, with --metadata required for chmod and chown while modification time is applied by the normal directory workflow. This issue is fixed in version 1.75.1.
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Analysis
by VulDB Data Team • 09/10/2026
The vulnerability identified in rclone versions prior to 1.75.1 represents a significant security flaw within the local backend implementation, specifically affecting operations involving symbolic links and metadata manipulation. Rclone is widely utilized for synchronizing data across various cloud storage providers, but its local filesystem handling contains logic errors that allow an attacker with control over source contents to bypass intended confinement mechanisms. The core issue arises when the tool operates in link mode using the --links flag. In this configuration, if a source directory contains a .rclonelink object designed as a symbolic link pointing outside the designated destination root, rclone incorrectly processes subsequent metadata operations on that path without verifying whether the target remains within the allowed boundaries.
The technical flaw lies in how specific functions handle translated links and file attributes. When Directory.translatedLink is false, which occurs under certain conditions during synchronization, the functions MkdirMetadata, writeMetadataToFile, and setTimes proceed to execute system calls such as os.Chown, os.Chmod, os.Chtimes, and birth-time handling directly on the path provided by the symlinked object. These operations are not properly confined within the root directory specified for the destination. Consequently, if an attacker controls the source archive or directory structure being synchronized, they can craft a scenario where these metadata-setting functions follow the symbolic link to apply changes to files or directories located outside the intended sandbox. This effectively breaks out of the os.Root confinement that is supposed to restrict file system access to specific areas for security and operational integrity.
The operational impact of this vulnerability allows an attacker with write access to source content to modify ownership, permissions, modification times, or birth times on arbitrary files within the host operating system where rclone is executed. While applying chmod and chown requires the explicit use of --metadata flags in some contexts, the application of modification times can be triggered through standard directory workflows without additional special arguments. This means that even routine synchronization tasks can inadvertently lead to privilege escalation or file tampering on sensitive system files if an attacker has previously planted malicious link structures in a source location accessed by rclone. The ability to alter permissions and ownership outside the destination root poses severe risks, including potential denial of service through permission changes on critical binaries or unauthorized access via modified ACLs on sensitive data stores.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the application fails to adequately validate that symbolic link targets remain within the expected directory structure before performing metadata operations. It also relates to CWE-73 External Control of File Name or Path, specifically regarding path traversal via symlink following during file system manipulation. In terms of attack vectors and tactics, this behavior is consistent with ATT&CK technique T1083 File and Directory Discovery combined with privilege escalation methods that rely on manipulating file attributes to gain unauthorized control over system resources. The lack of strict boundary enforcement for symbolic links in the local backend creates a pathway for lateral movement or persistence if an attacker can influence source inputs fed into rclone processes running with elevated privileges.
To mitigate this risk, organizations must immediately upgrade rclone to version 1.75.1 or later, where these logic errors have been corrected and proper confinement checks are enforced before executing metadata operations on symlinked paths. Until the update is applied, administrators should avoid using the --links flag in conjunction with untrusted source directories. Additionally, running rclone processes under restricted user accounts with minimal permissions can limit the potential damage of any successful exploitation attempt by reducing the scope of files that can be modified even if confinement is bypassed. Security teams should also audit existing automation scripts and CI/CD pipelines for usage patterns involving local synchronization to ensure no untrusted data sources are being processed through vulnerable versions of the tool.