CVE-2026-70458 in Rsync
Summary
by MITRE • 08/13/2026
rsync 3.0.0 before 3.5.0 contains an out-of-bounds write vulnerability that allows attackers to corrupt memory by triggering HLINK_BUMP processing on file entries with the FLAG_HLINKED flag set while the hard-link preservation option is inactive. Attackers can exploit the missing F_SUM field in the file_struct layout to access memory past the end of the allocated structure, corrupting adjacent heap or stack data.
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Analysis
by VulDB Data Team • 08/13/2026
The vulnerability under analysis represents a critical out-of-bounds write flaw affecting rsync versions prior to 3.5.0, specifically within the HLINK_BUMP processing mechanism. This issue arises when the software handles file entries that possess the FLAG_HLINKED flag while operating without active hard-link preservation functionality. The technical root cause stems from an insufficient validation mechanism during file structure processing, where the system fails to properly verify buffer boundaries before writing data into memory regions. The flaw manifests through a missing F_SUM field within the file_struct data layout, creating a predictable memory access pattern that allows attackers to traverse beyond allocated structure boundaries.
The operational impact of this vulnerability extends beyond simple memory corruption, as it provides attackers with potential pathways for arbitrary code execution or system compromise. When processing file entries with the specific flag combination, the software's memory management routines fail to account for the absence of proper boundary checks, enabling malicious actors to manipulate heap or stack data through controlled input manipulation. This type of vulnerability falls under the CWE-787 category of out-of-bounds write conditions, which are particularly dangerous because they can lead to denial of service, information disclosure, or complete system compromise depending on the execution environment and attack vector employed.
The exploitation scenario requires attackers to craft specific file entries that trigger the HLINK_BUMP processing path while maintaining the FLAG_HLINKED status without hard-link preservation active. This creates a precise condition where memory access patterns can be manipulated to overwrite adjacent data structures, potentially corrupting critical system memory regions or injecting malicious code into running processes. The vulnerability's severity is amplified by its potential integration with other attack techniques that might leverage the corrupted memory state to escalate privileges or bypass security controls.
Security mitigation strategies should prioritize immediate deployment of rsync version 3.5.0 or later, which contains the necessary patches addressing the boundary checking deficiencies in HLINK_BUMP processing. Organizations should also implement network segmentation and access controls to limit exposure of rsync services to untrusted networks, while monitoring for anomalous file transfer patterns that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1059.007 for execution through scripting languages and potentially T1068 for privilege escalation if exploited successfully, making comprehensive network monitoring essential for early detection of compromise attempts.
Additional protective measures include implementing strict input validation on file transfer operations, enabling heap protection mechanisms such as stack canaries or address space layout randomization, and conducting regular security assessments of file synchronization infrastructure. The vulnerability demonstrates the importance of proper memory management in network services and highlights how seemingly minor structural gaps in data layouts can create significant security risks when combined with specific operational conditions. Organizations should also consider implementing automated patch management systems to ensure rapid deployment of security updates across all rsync installations within their infrastructure, particularly given the widespread use of this file synchronization utility in enterprise environments.