CVE-2018-20375 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 sym_pop function in tccgen.c.
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Analysis
by VulDB Data Team • 04/23/2020
The vulnerability identified as CVE-2018-20375 represents a critical memory corruption flaw within the Tiny C Compiler version 0.9.27, a lightweight compiler designed for rapid compilation and execution of C code. This issue manifests as an out-of-bounds write condition that occurs during the compilation process when processing specifically crafted source files, making it particularly dangerous for environments where untrusted code might be compiled or processed. The vulnerability resides within the sym_pop function located in the tccgen.c source file, which is responsible for managing symbol table operations during compilation.
The technical implementation of this flaw involves an 8-byte out-of-bounds write operation that occurs when the compiler attempts to manipulate symbol table entries during code compilation. This type of memory corruption vulnerability falls under the Common Weakness Enumeration category CWE-787, which specifically addresses out-of-bounds write conditions that can lead to arbitrary code execution or system instability. The sym_pop function fails to properly validate array bounds when accessing symbol table elements, allowing an attacker to write data beyond the allocated memory boundaries. This particular memory corruption vector represents a classic buffer overflow scenario where the compiler's internal data structures are not adequately protected against malicious input.
The operational impact of CVE-2018-20375 extends beyond simple compilation failures, as it can potentially enable remote code execution when the compiler processes untrusted source code. Attackers who can influence the compilation process or submit malicious code for compilation can exploit this vulnerability to overwrite adjacent memory locations, potentially corrupting critical program data or executing arbitrary code. The vulnerability is particularly concerning in build environments, continuous integration systems, or any scenario where third-party code is compiled using the affected version of TinyCC. From an adversary perspective, this vulnerability aligns with ATT&CK technique T1059.007 for execution through command and scripting interpreter, and T1203 for exploitation of known vulnerabilities in compilation tools.
Mitigation strategies for this vulnerability should prioritize immediate patching of TinyCC installations to versions that address the out-of-bounds write condition in the sym_pop function. Organizations should implement strict code review processes for any source code compiled using TinyCC, particularly when dealing with untrusted inputs. Additionally, sandboxing compilation environments and implementing memory protection mechanisms such as stack canaries or address space layout randomization can help reduce the exploitability of this vulnerability. The fix typically involves adding proper bounds checking within the sym_pop function to ensure that memory accesses remain within allocated boundaries, preventing the 8-byte write operation from exceeding valid memory limits and maintaining the integrity of the compiler's internal state.