CVE-2018-20376 in Tiny C Compiler
Summary
by MITRE
An issue was discovered in Tiny C Compiler (aka TinyCC or TCC) 0.9.27. Compiling a crafted source file leads to an 8 byte out of bounds write in the asm_parse_directive function in tccasm.c.
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Analysis
by VulDB Data Team • 04/23/2020
The vulnerability identified as CVE-2018-20376 represents a critical memory corruption flaw within the Tiny C Compiler version 0.9.27. This issue manifests as an out-of-bounds write operation that occurs during the compilation process when handling maliciously crafted source code. The Tiny C Compiler, commonly known as TCC, is a lightweight C compiler designed for rapid compilation and execution, making it popular in embedded systems and development environments where quick prototyping is essential. However, this particular vulnerability undermines the compiler's safety mechanisms and creates potential attack vectors that could be exploited by adversaries.
The technical flaw resides specifically within the asm_parse_directive function located in the tccasm.c source file. This function is responsible for parsing assembly directives during the compilation process, and when processing malformed input, it fails to properly validate array bounds before writing data. The vulnerability manifests as an 8-byte out-of-bounds write, indicating that the compiler attempts to write more data than allocated buffer space, potentially overwriting adjacent memory locations. This type of flaw falls under the CWE-787 weakness category, which specifically addresses out-of-bounds write vulnerabilities that can lead to arbitrary code execution or system instability.
The operational impact of this vulnerability extends beyond simple compilation failures, as it creates a potential pathway for remote code execution when the compiler processes untrusted input. Attackers could craft malicious source files that, when compiled by TCC, would trigger the out-of-bounds write condition. This scenario is particularly concerning given TCC's widespread use in development environments, automated build systems, and embedded applications where untrusted code might be compiled. The vulnerability could be exploited in continuous integration pipelines, development environments, or any system where TCC is used to compile user-provided code, potentially allowing attackers to execute arbitrary commands on the compilation host. According to ATT&CK framework, this vulnerability maps to the T1059.007 technique for execution through command and scripting interpreter, as successful exploitation would enable attackers to execute code through the compromised compilation environment.
Mitigation strategies for CVE-2018-20376 should focus on immediate patching of the TCC compiler to version 0.9.28 or later, which contains the necessary fixes for the buffer overflow condition. Organizations should also implement strict input validation measures when processing source code through TCC, particularly in automated environments where user input is involved. Additional protective measures include running the compiler in restricted environments with limited privileges, implementing sandboxing techniques, and ensuring that only trusted code is compiled using TCC. Regular security audits of compilation environments and monitoring for unusual compilation activities can help detect potential exploitation attempts. System administrators should also consider updating their build processes to use more robust compilers with better memory safety guarantees, particularly in environments where security is paramount. The vulnerability demonstrates the importance of memory safety in compiler development and highlights how seemingly minor flaws in parsing functions can have significant security implications across the entire software development lifecycle.