CVE-2026-71266 in tinyobjloader-c
Summary
by MITRE • 08/05/2026
tinyobjloader-c's tinyobj_parse_and_index_mtl_file() (tinyobj_loader_c.h) reads each line of a .mtl material file into a fixed 4096-byte stack buffer `linebuf` via memcpy(linebuf, p, p_len), guarded only by `assert(p_len < 4095)`. Because assert() compiles to a no-op under -DNDEBUG (standard for release builds), a crafted .mtl file containing a line (e.g. a "newmtl" material name) longer than 4096 bytes overflows linebuf into the adjacent stack variable namebuf and beyond, corrupting the stack of any application that loads attacker-supplied 3D model/material files. The identical vulnerable pattern is duplicated in a second function in the same file.
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Analysis
by VulDB Data Team • 08/05/2026
The vulnerability in tinyobjloader-c's tinyobj_parse_and_index_mtl_file() function represents a classic buffer overflow condition that exploits improper input validation mechanisms within stack-based memory management. This flaw exists in the material file parsing functionality where each line from .mtl files is read into a fixed 4096-byte stack buffer named linebuf without adequate bounds checking beyond a simple assert statement. The implementation pattern demonstrates a fundamental misunderstanding of security considerations in release builds where debug assertions are disabled, creating an exploitable condition that can be leveraged by attackers to corrupt application memory.
The technical execution of this vulnerability relies on the standard compilation behavior where assert() macros compile to no-ops when -DNDEBUG is enabled, which is the typical configuration for production releases. When a maliciously crafted .mtl file contains a line exceeding 4096 bytes, specifically targeting elements like "newmtl" material names that can be arbitrarily long, the memcpy operation overflows the designated stack buffer into adjacent memory locations including the namebuf variable and potentially beyond. This stack corruption directly compromises the application's memory layout and execution flow, creating opportunities for arbitrary code execution or denial of service conditions.
The operational impact of this vulnerability extends across any application that integrates tinyobjloader-c for 3D model parsing, particularly those handling untrusted user input or third-party assets without proper validation. The flaw affects not just individual applications but represents a systemic risk in software ecosystems where such loaders are commonly embedded, as the attack surface includes any 3D content processing pipeline that accepts external material files. This vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows occurring in stack memory regions due to inadequate bounds checking.
The identical vulnerable pattern appears in a second function within the same file, indicating a systemic code quality issue rather than an isolated incident. This duplication suggests that developers may have copied problematic code patterns without proper security review or that the underlying parsing architecture was not designed with memory safety as a primary consideration. The presence of multiple instances increases the probability of exploitation and reduces the effectiveness of any partial mitigations. From an attacker's perspective, this vulnerability maps directly to ATT&CK technique T1059.007 Command and Scripting Interpreter: PowerShell, as it creates a condition where untrusted input can be used to manipulate stack memory during parsing operations.
Mitigation strategies must address both immediate code-level fixes and broader architectural considerations for secure input handling in 3D asset processing applications. The primary solution involves implementing proper bounds checking that functions correctly regardless of compilation flags, replacing the assert-based validation with explicit length verification that prevents buffer overflows even in release builds. Applications should also implement input sanitization procedures for material files, including line length limits and file size constraints. Additionally, developers should consider adopting modern memory-safe programming practices or libraries that provide automatic bounds checking to prevent similar vulnerabilities in future implementations.