CVE-2026-53794 in Rsync
Summary
by MITRE • 08/13/2026
rsync before 3.5.0 contains a logic error in --max-alloc handling that allows a sender or configuration setting --max-alloc=0 to disable allocation sanity checks entirely rather than enforcing a zero-byte cap. Attackers can exploit this flaw to cause the receiver to attempt unbounded memory allocations for file list and data structures, potentially exhausting available memory and causing a denial of service.
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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 logic error within the --max-alloc parameter handling mechanism that fundamentally undermines the software's memory management safeguards. This flaw exists in the implementation of the maximum allocation limit functionality, where the system fails to properly enforce the intended memory constraints when the --max-alloc=0 parameter is utilized. The vulnerability stems from a design oversight in how the software processes this specific configuration setting, creating an unintended pathway for bypassing essential memory allocation sanity checks that are crucial for maintaining system stability and preventing resource exhaustion attacks.
The technical execution of this vulnerability occurs through the manipulation of the --max-alloc parameter during rsync operations, where attackers can deliberately set this value to zero to disable critical memory allocation validation mechanisms. When processed incorrectly, the system fails to enforce the zero-byte cap that should normally prevent excessive memory consumption, instead allowing the receiver component to proceed with unbounded memory allocations for essential file list and data structures. This logical error creates a scenario where the rsync process can consume unlimited memory resources without proper bounds enforcement, effectively transforming what should be a controlled resource allocation into an unrestricted memory consumption pattern.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise entire system stability and availability. Attackers can exploit this flaw by initiating rsync transfers with maliciously configured --max-alloc parameters, causing the target system to allocate memory without bounds until system resources are exhausted. This memory exhaustion can lead to complete system instability, process termination, and broader service disruption across multiple applications that depend on available system memory for their operations. The vulnerability particularly affects systems running rsync in server mode or those handling large file transfers where the memory consumption patterns can rapidly escalate beyond normal operational limits.
From a cybersecurity perspective, this vulnerability maps directly to CWE-770, which addresses allocation of resources without proper limit enforcement, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. The flaw represents a classic example of improper input validation where the system fails to properly validate configuration parameters before applying them to critical resource management functions. Organizations utilizing rsync in production environments face significant risk exposure, particularly in scenarios involving untrusted file transfers or automated synchronization processes where attackers might inject malicious parameter values. The vulnerability demonstrates how seemingly innocuous configuration options can become attack vectors when proper validation and enforcement mechanisms are absent from the implementation.
Mitigation strategies for this vulnerability require immediate patching to rsync version 3.5.0 or later, which contains the corrected implementation of --max-alloc handling. System administrators should also implement strict parameter validation at the network level, particularly in environments where rsync is exposed to untrusted users or external systems. Additional protective measures include implementing resource limits through operating system controls such as ulimit settings or containerization policies that restrict memory consumption for rsync processes. Regular security monitoring and log analysis should be employed to detect anomalous memory usage patterns that might indicate exploitation attempts, while network segmentation can help limit the potential impact of successful attacks by isolating critical systems from potentially compromised environments.