0xiviel/poc-armnn-onnxparser-oob

Arm NN OnnxParser Reshape OOB Write (CWE-787)

Vulnerability

Root cause: OnnxParser.cpp:2332 in ParseReshape() uses std::vector::reserve() instead of resize() when building target shape dimensions from an ONNX model.

reserve() allocates capacity but does NOT change size(), which remains 0. The subsequent loop writes shape values via targetShape[i] — accessing indices past size() is undefined behavior per the C++ standard, regardless of capacity.

Vulnerable Code

// OnnxParser.cpp:2328-2338
std::vector<unsigned int> targetShape;           // size = 0
targetShape.reserve(dims);                       // capacity = dims, size STILL 0!
for(uint i = 0; i < dims; i++)
{
    targetShape[i] = static_cast<unsigned int>(val);  // OOB WRITE!
}

Two Distinct Issues

1. OOB Write (UB) — writing to unconstructed elements past size()
2. Wrong TensorShape — at line 2379, targetShape.size() is still 0, constructing a 0-dimension TensorShape regardless of actual model shape

Impact

• CWE-787 (Out-of-bounds Write)
• CVSS 7.5 (High)
• Affects any ONNX model with Reshape operations (nearly all models)
• Deployed on millions of embedded/mobile devices

Fix

-        targetShape.reserve(dims);
+        targetShape.resize(dims);