CVE-2026-70459 in Rsync
Summary
by MITRE • 08/13/2026
rsync 3.0.0 before 3.5.0 contains a null pointer dereference vulnerability in the daemon child process that allows remote attackers to crash the daemon by sending a file list whose first entry is a dot entry not typed as a directory. The daemon dereferences the first file list entry as a directory structure pointer without verifying the entry type, resulting in an invalid or uninitialized pointer dereference that terminates the client connection.
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Analysis
by VulDB Data Team • 08/13/2026
This vulnerability exists within rsync versions prior to 3.5.0 and represents a critical null pointer dereference flaw in the daemon child process execution path. The issue manifests when remote attackers send malicious file list data containing a dot entry that is not properly typed as a directory structure. The daemon process fails to validate the entry type before attempting to dereference the first file list entry as a directory structure pointer, creating an invalid memory access condition that causes the service to crash and terminate client connections.
The technical implementation of this vulnerability stems from inadequate input validation within the rsync daemon's file list processing routine. When the daemon receives a file list from a remote client, it processes each entry in sequence without proper type checking for the initial entry. The dot entry specifically triggers this condition because the code path assumes all entries are properly typed directory structures, but when a dot entry is present without explicit directory typing, the dereference operation attempts to access memory through an uninitialized or null pointer reference.
This vulnerability directly maps to CWE-476 which defines null pointer dereference conditions in software implementations. The operational impact of this flaw extends beyond simple service disruption as it enables remote denial of service attacks against rsync daemon services. Attackers can exploit this weakness by establishing connections to rsync daemons and sending crafted file lists that contain the specific malformed dot entry pattern, resulting in immediate service termination and client disconnection. The vulnerability affects systems running rsync versions between 3.0.0 and 3.4.9 inclusive, making it particularly concerning for organizations maintaining older rsync installations.
The attack vector operates through standard network communication channels where attackers can connect to rsync daemon services and submit malicious file list entries without requiring authentication or elevated privileges. This remote exploitation capability makes the vulnerability especially dangerous in environments where rsync daemons are exposed to untrusted networks or internet-facing services. The lack of proper input sanitization and type validation creates a persistent threat surface that can be exploited repeatedly by attackers seeking to disrupt rsync operations.
Mitigation strategies should focus on immediate version upgrades to rsync 3.5.0 or later where the vulnerability has been addressed through proper input validation mechanisms. Organizations should also implement network segmentation to limit access to rsync daemon services, deploy intrusion detection systems to monitor for suspicious file list patterns, and consider implementing additional access controls such as firewall rules that restrict rsync connections to trusted networks only. The fix implemented in newer versions involves adding proper type checking before dereferencing file list entries, ensuring that directory structure pointers are validated before memory access operations occur.
From a cybersecurity perspective, this vulnerability demonstrates the importance of proper input validation and defensive programming practices in network services. The ATT&CK framework categorizes this as a denial of service attack technique through software exploitation, specifically targeting service availability by leveraging implementation flaws in daemon processes. Organizations should conduct thorough inventory assessments to identify all systems running vulnerable rsync versions and implement patch management procedures that prioritize security updates for critical infrastructure components. Regular security testing including vulnerability scanning and penetration testing should be performed to identify similar weaknesses in other network services that may exhibit comparable null pointer dereference patterns.
The remediation process requires careful consideration of deployment timing to avoid service disruption during patching operations, particularly in production environments where rsync services may be actively used for data synchronization. System administrators should test patches in staging environments before rolling out updates to production systems, and maintain rollback procedures in case patch installation introduces unexpected compatibility issues. Additionally, monitoring solutions should be configured to detect unusual connection patterns or service termination events that may indicate exploitation attempts against this vulnerability.
This vulnerability serves as a reminder of the critical need for continuous security maintenance and the potential impact of seemingly minor implementation flaws on overall system security posture. The rsync daemon's exposure to remote attack surfaces requires ongoing vigilance and proactive security measures to prevent exploitation by threat actors seeking to disrupt file synchronization services and potentially gain access to sensitive data environments.