CVE-2021-32490 in DjVuLibre
Summary
by MITRE • 06/25/2021
A flaw was found in djvulibre-3.5.28 and earlier. An out of bounds write in function DJVU::filter_bv() via crafted djvu file may lead to application crash and other consequences.
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Analysis
by VulDB Data Team • 07/02/2021
The vulnerability identified as CVE-2021-32490 resides within the djvulibre library version 3.5.28 and earlier, representing a critical out-of-bounds write flaw in the DJVU::filter_bv() function. This issue manifests when processing maliciously crafted djvu files, creating a pathway for arbitrary code execution or system compromise. The flaw stems from inadequate input validation and bounds checking within the image processing pipeline of the djvu file format parser, where the application fails to properly verify array indices before writing data to memory locations.
The technical nature of this vulnerability places it firmly within CWE-787: Out-of-bounds Write, a well-documented weakness that occurs when a program writes data past the end of a buffer or array. This specific implementation flaw allows attackers to manipulate the memory layout of the djvulibre library by constructing specially formatted djvu files that trigger the vulnerable code path. When the DJVU::filter_bv() function processes these crafted inputs, it fails to validate the boundaries of memory allocations, enabling an attacker to overwrite adjacent memory regions with controlled data.
Operationally, this vulnerability presents significant risks to systems that process djvu documents, including document management systems, digital libraries, email servers, and content delivery platforms. The impact extends beyond simple application crashes to potentially enable remote code execution, privilege escalation, or denial of service conditions. Attackers can exploit this flaw by embedding malicious djvu files in web applications, email attachments, or file sharing systems, where the vulnerable library automatically processes these files during normal operation. The vulnerability's exploitation aligns with ATT&CK technique T1203: Exploitation for Client Execution, as it leverages the legitimate document processing functionality to achieve malicious objectives.
Systems utilizing djvulibre versions prior to 3.5.29 are at risk, particularly those that automatically process or render djvu files without proper sanitization. The vulnerability's exploitation requires minimal user interaction, as simply opening or processing a malicious djvu file can trigger the out-of-bounds write condition. Organizations should prioritize patching their djvulibre installations to version 3.5.29 or later, which includes proper bounds checking and input validation mechanisms. Additional mitigations include implementing strict file format validation, sandboxing document processing operations, and deploying network-based intrusion detection systems to monitor for exploitation attempts. The vulnerability demonstrates the critical importance of input validation in multimedia processing libraries and highlights the potential for remote code execution in widely deployed document handling components.