Impact Analysis

This vulnerability can be triggered by a user opening a maliciously crafted STL file. The impacts include denial of service (DoS), where the application may crash or become unstable due to the out-of-bounds memory access.

Additionally, there is a possibility of information disclosure, where sensitive data from adjacent memory could be read unintentionally due to the out-of-bounds read.

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Executive Summary

CVE-2026-42476 is a memory safety vulnerability in Open CASCADE Technology (OCCT) related to its STL ASCII file parser. Specifically, it involves two heap-based out-of-bounds read issues in the function RWStl_Reader::ReadAscii. The problem arises because buffers returned by the ReadLine function are not properly checked for their length before being used in string comparison or direct byte access operations.

An attacker can exploit this by crafting an STL file with extremely short lines that cause the ReadLine function to return very small buffers (1-3 bytes). Since the code does not validate the length of these buffers before parsing, it can read beyond the allocated memory, leading to out-of-bounds reads.

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Detection Guidance

This vulnerability can be detected by using AddressSanitizer (ASAN) or similar memory safety tools to monitor for out-of-bounds reads when processing STL files with the affected Open CASCADE Technology (OCCT) versions.

Specifically, running the OCCT STL ASCII file parser on crafted STL files that contain extremely short lines (1-3 bytes) can trigger the vulnerability and cause ASAN to detect the out-of-bounds read.

A suggested approach is to use a proof-of-concept STL file known to trigger the issue and run the OCCT tool under ASAN or another memory error detector to observe any memory violations.

• Use AddressSanitizer (ASAN) to run the OCCT STL parser: compile OCCT with ASAN enabled and process suspicious STL files.
• Monitor logs or error outputs for out-of-bounds read errors during file parsing.

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Mitigation Strategies

Immediate mitigation involves validating the length of buffers returned by the ReadLine function before any parsing or memory access operations.

Until a patched version of OCCT is applied, avoid opening or processing untrusted or suspicious STL files that may contain extremely short lines designed to trigger the vulnerability.

Applying updates or patches that include the fix—validating the ReadLine return length before proceeding—is the recommended long-term solution.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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