CVE-2026-9535 in VTK
Summary
by MITRE • 10/29/2026
A out-of-bounds read vulnerability exists in the vtkChacoReader InputGraph2 functionality of vtk (version(s): 9.6.1). A specially crafted chaco can lead to an out-of-bounds read. An attacker can provide a malicious file to trigger this vulnerability.
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Analysis
by VulDB Data Team • 10/29/2026
The VTK library, specifically within the version range including 9.6.1, contains a critical memory safety flaw in its vtkChacoReader component. This open-source software is widely used for scientific visualization and processes various data formats, including the Chaco graph format. The vulnerability resides in the InputGraph2 functionality of this reader module. When processing input files formatted according to the Chaco specification, the application fails to adequately validate array indices or buffer boundaries before accessing memory locations. This lack of rigorous bounds checking allows for an out-of-bounds read condition when a specially crafted file is supplied as input. The flaw represents a classic instance of improper access control over allocated memory resources, where the software attempts to retrieve data from a location that lies outside the intended operational range of the buffer.
From a technical perspective, this vulnerability aligns with Common Weakness Enumeration (CWE) identifier CWE-125, which describes out-of-bounds read operations. In such scenarios, an attacker can construct a malicious Chaco file containing specific structural anomalies or malformed data fields that cause the parser to calculate incorrect memory offsets. When the vtkChacoReader processes this crafted input, it reads from memory addresses beyond the allocated buffer limits. While out-of-bounds reads are often less immediately destructive than write vulnerabilities because they do not directly alter program state, they pose significant risks related to information disclosure and potential denial of service. The read operation may retrieve sensitive data stored in adjacent memory regions, such as stack variables or other objects within the same process space. Furthermore, if the retrieved out-of-bounds value is subsequently used for control flow decisions or further memory operations, it could lead to undefined behavior, application crashes, or exploitation chains that leverage subsequent vulnerabilities like use-after-free conditions.
The operational impact of this vulnerability depends heavily on how VTK is integrated into end-user applications. If a visualization tool utilizes the vtkChacoReader and allows users to open arbitrary Chaco files without sufficient sanitization, an attacker could trick a victim into opening a malicious file. This action would trigger the out-of-bounds read within the context of the application process. The immediate consequence typically manifests as data corruption or program instability, leading to crashes that disrupt workflow and cause denial of service for legitimate users. In more sophisticated attack scenarios, particularly if the vulnerable code is part of a server-side processing pipeline or an automated analysis tool, the attacker might extract confidential information from memory dumps or logs generated during the crash. This could include cryptographic keys, user credentials, or proprietary scientific data being processed by the visualization software at that moment.
To mitigate this risk, developers and users must prioritize updating to patched versions of VTK where the bounds checking logic in InputGraph2 has been corrected. The fix typically involves implementing strict validation checks before any memory access occurs, ensuring that all indices are within the valid range of the allocated buffer. For organizations relying on older or unpatched versions, it is advisable to implement input sanitization at the application layer, rejecting files with suspicious structures or unexpected sizes before they reach the vulnerable reader component. Additionally, enabling compiler-based security features such as AddressSanitizer during development and testing phases can help detect such memory errors early in the software lifecycle. Security teams should also monitor for any indicators of compromise related to unusual memory access patterns or crashes within applications that depend on VTK's Chaco file handling capabilities.
This vulnerability is categorized under ATT&CK technique T1083, which covers File and Directory Discovery, as it involves reading data from a specific file format in an unintended manner. It also relates to the broader category of memory corruption vulnerabilities often exploited for information gathering or destabilizing target systems. The severity is generally considered moderate due to the read-only nature of the flaw, but its potential for chaining with other weaknesses makes it a significant concern for security-conscious deployments. Continuous monitoring and timely patching remain the most effective defenses against exploitation attempts targeting this specific component within the VTK ecosystem.