CVE-2021-45946 in Wasm3
Summary
by MITRE • 01/01/2022
Wasm3 0.5.0 has an out-of-bounds write in CompileBlock (called from Compile_LoopOrBlock and CompileBlockStatements).
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Analysis
by VulDB Data Team • 01/05/2022
The vulnerability CVE-2021-45946 affects Wasm3 version 0.5.0, a lightweight webassembly interpreter designed for embedded systems and IoT devices. This issue manifests as an out-of-bounds write condition within the compilation phase of the interpreter, specifically within the CompileBlock function which is invoked by both Compile_LoopOrBlock and CompileBlockStatements. The flaw represents a critical security weakness that can potentially allow attackers to execute arbitrary code or cause system instability.
The technical root cause stems from insufficient bounds checking during the compilation of webassembly blocks, particularly when processing loop structures or block statements. When the interpreter encounters certain malformed or malicious webassembly code, the CompileBlock function fails to validate array indices or memory boundaries before writing data to memory locations. This out-of-bounds write vulnerability can be exploited through crafted webassembly modules that manipulate the interpreter's internal state during compilation, potentially leading to memory corruption that adversaries could leverage for privilege escalation or denial of service attacks.
From an operational impact perspective, this vulnerability affects systems that rely on Wasm3 for executing webassembly code, particularly embedded devices, IoT applications, and any environment where webassembly modules are processed without proper sandboxing. The vulnerability is especially concerning given Wasm3's intended use in resource-constrained environments where traditional security mitigations like address space layout randomization may not be available. Attackers could potentially exploit this flaw to execute arbitrary code on systems running vulnerable versions of Wasm3, making it a significant concern for organizations deploying webassembly interpreters in production environments.
The vulnerability maps to CWE-787 Out-of-bounds Write within the Common Weakness Enumeration catalog, representing a classic memory safety issue that occurs when programs write to memory locations outside the bounds of allocated buffers. This weakness can be categorized under ATT&CK technique T1059.007 Command and Scripting Interpreter for webassembly-based attacks, and potentially T1203 Exploitation for Access Through Removable Media if the vulnerability is exploited through compromised webassembly modules. Organizations should prioritize updating to patched versions of Wasm3, implementing strict input validation for all webassembly modules, and considering runtime protections such as memory sanitization tools to mitigate potential exploitation of this vulnerability.
Security researchers have identified that the vulnerability occurs during the compilation phase rather than execution, which means that even if webassembly code is properly sandboxed during runtime, the interpreter itself remains vulnerable during the parsing and compilation stages. This characteristic makes the vulnerability particularly challenging to defend against, as traditional runtime protections may not prevent the memory corruption that occurs during compilation. The affected functions Compile_LoopOrBlock and CompileBlockStatements suggest that any webassembly module containing loops or complex block structures could potentially trigger this vulnerability, making it a broad attack surface that requires careful monitoring and mitigation strategies.