CVE-2026-53798 in rsync
Summary
by MITRE • 08/13/2026
rsync tbefore 3.5.0 contains a privilege confusion vulnerability in the name-converter subprocess uid/gid mapping that allows local attackers to cause transferred files to be owned by root by influencing name-converter responses to return empty values. When the name-converter subprocess returns an empty response for a uid or gid lookup, rsync incorrectly interprets it as a successful resolution to uid/gid 0 (root) rather than a lookup failure, and if the name-converter also signals fake super-user status, rsync proceeds with root ownership assignments for transferred files.
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Analysis
by VulDB Data Team • 08/13/2026
The vulnerability in rsync versions prior to 3.5.0 represents a critical privilege confusion flaw that undermines the integrity of file ownership management during data transfers. This issue stems from improper handling of uid/gid mapping within the name-converter subprocess, creating a scenario where local attackers can manipulate file ownership to be assigned to the root user. The vulnerability specifically manifests when the name-converter subprocess returns empty responses for uid or gid lookups, which rsync incorrectly interprets as successful resolution to uid/gid 0 rather than as lookup failures. This misinterpretation creates a security boundary violation where legitimate system protections are bypassed through manipulation of subprocess responses.
The technical implementation of this vulnerability involves the name-converter subprocess functionality that handles user and group identifier resolution during file transfers. When rsync processes file transfers, it relies on this subprocess to map usernames and group names to their corresponding numeric identifiers. The flaw occurs in the error handling logic where empty responses from the name-converter are not properly validated against expected failure conditions. Instead of treating empty uid/gid responses as authentication failures requiring fallback mechanisms, the code path assumes successful root-level resolution, leading to privilege escalation through file ownership manipulation.
Operational impact assessment reveals that this vulnerability enables local attackers to gain unauthorized control over file ownership during rsync operations, potentially allowing them to modify system-critical files with elevated privileges. The attack vector requires local access to the system and the ability to influence or manipulate the name-converter subprocess responses, making it particularly dangerous in environments where rsync is used for system administration tasks. When combined with scenarios where the name-converter signals fake super-user status, the vulnerability becomes even more severe as it allows complete control over file ownership assignments, potentially enabling persistent backdoor creation or system compromise through carefully crafted file transfers.
Security implications extend beyond immediate privilege escalation to encompass broader system integrity concerns and potential chain reactions within networked environments. The flaw aligns with CWE-284 (Improper Access Control) and CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) categories, representing a combination of access control failure and improper privilege handling. From an ATT&CK framework perspective, this vulnerability maps to T1068 (Exploitation for Privilege Escalation) and T1548.001 (Abuse Elevation Control Mechanism), as it enables attackers to manipulate system-level permissions through legitimate system tools. The vulnerability also demonstrates characteristics of T1497 (Virtualization/Sandbox Evasion) when considering potential exploitation in containerized or virtualized environments where rsync operations are common.
Mitigation strategies should focus on immediate patching to rsync version 3.5.0 or later, which addresses the core uid/gid mapping logic by properly validating empty responses and implementing stricter error handling for name-converter subprocess interactions. System administrators should also implement monitoring controls to detect unusual file ownership changes during rsync operations and consider restricting local access to rsync processes where possible. Additional protective measures include implementing proper privilege separation between rsync operations and system-level uid/gid resolution, ensuring that subprocess responses are validated through multiple verification mechanisms rather than relying on single-point interpretation of empty values. Organizations should also review their rsync configurations and access controls to minimize potential attack surface exposure while maintaining legitimate operational functionality.