CVE-2021-25832 in DocumentServer
Summary
by MITRE • 03/02/2021
A heap buffer overflow vulnerability inside of BMP image processing was found at [core] module of ONLYOFFICE DocumentServer v4.0.0-9-v6.0.0. Using this vulnerability, an attacker is able to gain remote code executions on DocumentServer.
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Analysis
by VulDB Data Team • 03/14/2021
The heap buffer overflow vulnerability identified as CVE-2021-25832 resides within the core module of ONLYOFFICE DocumentServer version 4.0.0-9 through 6.0.0, specifically affecting BMP image processing functionality. This vulnerability represents a critical security flaw that can be exploited to achieve remote code execution on the affected system. The issue manifests when the application processes malformed BMP image files, creating conditions where memory operations exceed allocated buffer boundaries. Such buffer overflows typically occur when input validation is insufficient and the application fails to properly verify the size and structure of incoming image data before processing.
The technical implementation of this vulnerability involves improper bounds checking during BMP image parsing operations, where the application allocates heap memory for image data structures without adequate validation of input parameters. When an attacker crafts a malicious BMP file with oversized or malformed headers, the parsing routine can write beyond the allocated memory boundaries, potentially overwriting adjacent memory regions including function pointers, return addresses, or other critical program state information. This memory corruption directly enables attackers to manipulate program execution flow and potentially execute arbitrary code with the privileges of the DocumentServer process.
The operational impact of this vulnerability extends beyond simple remote code execution to encompass complete system compromise, as the DocumentServer typically runs with elevated privileges and may have access to sensitive data repositories, file systems, and network resources. Attackers exploiting this vulnerability can gain unauthorized access to documents, user data, and potentially use the compromised server as a pivot point for further attacks within the network infrastructure. The vulnerability affects organizations relying on ONLYOFFICE DocumentServer for document management and collaboration, making it particularly dangerous in enterprise environments where document processing is a core function.
Mitigation strategies should include immediate patching of the DocumentServer to versions that address the buffer overflow in BMP image processing, implementing strict input validation for all image file types, and deploying network segmentation to limit access to the DocumentServer. Organizations should also consider implementing application whitelisting controls, monitoring for anomalous file processing patterns, and conducting regular security assessments of document processing components. The vulnerability aligns with CWE-121 heap-based buffer overflow classification and represents a technique commonly mapped to ATT&CK tactics including execution through file and directory permissions, privilege escalation, and command and control communications. Network administrators should also consider deploying intrusion detection systems capable of identifying malicious BMP file patterns and implementing mandatory access controls to prevent unauthorized code execution in the DocumentServer environment.