Listen to this Post
The Vyper compiler, a Pythonic smart contract language for the Ethereum Virtual Machine, contains a memory corruption vulnerability that manifests when function calls are performed inside tuples or as arguments within other function calls. This issue, tracked as GHSA-2r3x-4mrv-mcxf and internally referenced as VVE-2020-0004, stems from the compiler generating an incorrect pointer to the tip of the stack during code generation for nested function calls. When a function call appears inside a tuple expression or is nested as an argument to another function call, the compiler’s stack management logic fails to correctly track the memory location, leading to corruption of data on the stack. The vulnerability specifically affects the compiler’s ability to properly allocate and reference memory slots when evaluating complex expressions involving multiple function invocations. This flaw was discovered during security research into the Vyper compiler’s code generation for tuple expressions and nested calls. The root cause lies in the `build_IR` function’s handling of function calls within tuple contexts, where the stack pointer is not properly updated after the inner call completes. As a result, subsequent operations within the same expression can read from or write to incorrect memory locations, corrupting valid data. The impact is particularly severe in smart contract environments where memory corruption can lead to incorrect state transitions, unexpected behavior, or exploitable conditions. The vulnerability was fixed in Vyper version 0.2.6 through pull request 2186, which corrected the stack pointer management for function calls within tuples and nested calls. A related but distinct issue involving function calls within arrays was later addressed in pull request 2345. Developers using Vyper versions prior to 0.2.6 are strongly advised to upgrade to the patched version to mitigate the risk of memory corruption in their smart contracts. The fix ensures that the compiler correctly tracks the stack tip after each nested function call, preventing the incorrect pointer dereference that causes memory corruption.
DailyCVE Form:
Platform: Vyper
Version: <0.2.6
Vulnerability: Memory corruption
Severity: Moderate
date: 2020-10-10
Prediction: Patched (v0.2.6)
What Undercode Say:
Check Vyper version vyper --version Install affected version (for testing) pip install vyper==0.2.5 Compile the example contract vyper -f bytecode example.vy Update to patched version pip install vyper==0.2.6
example.vy - Vulnerable code pattern @internal def _foo(a: uint256, b: uint256, c: uint256) -> (uint256, uint256, uint256, uint256, uint256): return 1, a, b, c, 5 @internal def _foo2() -> uint256: a: uint256[bash] = [6,7,8,9,10,11,12,13,15,16] return 4 @external def foo() -> (uint256, uint256, uint256, uint256, uint256): return self._foo(2, 3, self._foo2()) Nested call in tuple
Scan for vulnerable Vyper versions pip-audit --requirement requirements.txt Verify the fix in v0.2.6 git clone https://github.com/vyperlang/vyper.git cd vyper && git checkout v0.2.6 grep -r "stack tip" vyper/parser/
Exploit: (Educational Purposes!)
The vulnerability can be triggered by deploying a Vyper contract that contains function calls nested within tuples or used as arguments to other functions. An attacker could potentially exploit this by crafting specific contract logic that causes the compiler to generate bytecode with incorrect stack pointer management, leading to memory corruption at runtime. When the corrupted memory affects critical state variables such as balances, access controls, or conditional checks, the contract’s behavior becomes unpredictable and potentially exploitable. For educational purposes, security researchers can compile the vulnerable example contract using Vyper 0.2.5 and observe the generated bytecode for incorrect stack operations, then compare with the patched output from 0.2.6 to understand the fix.
Protection:
- Upgrade Vyper to version 0.2.6 or later immediately
- Audit existing smart contracts compiled with Vyper < 0.2.6 for patterns involving function calls inside tuples or nested calls
- Recompile and redeploy affected contracts using the patched compiler version
- Avoid using function calls as arguments within other function calls or inside tuple expressions in vulnerable compiler versions
- Use static analysis tools that can detect compiler-level vulnerabilities in smart contract bytecode
- Monitor Vyper security advisories for related issues such as VVE-2021-0001 involving function calls within arrays
Impact:
Successful exploitation of this memory corruption vulnerability can lead to incorrect contract execution, loss of funds, or unauthorized state modifications in affected smart contracts. The severity is rated moderate because exploitation requires specific code patterns and conditions, but the potential consequences in a blockchain environment are significant due to the immutable nature of deployed contracts.
🎯Let’s Practice Exploiting & Learn Patching For Free:
🎓 Live Courses & Certifications:
Join Undercode Academy for Verified Certifications
🚀 Request a Custom Project:
Secure, high-velocity infrastructure and disruptive technological engineering. Contact our engineering team for high-tier development and proprietary systems:
[email protected]
💎 Smart Architecture | 🛡️ Secure by Design | ⭐ Trusted by Thousands
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
