CVE-2023-42443
HIGHVyper vulnerable to memory corruption in certain builtins utilizing `msize`
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
vyperReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine (EVM). In version 0.3.9 and prior, under certain conditions, the memory used by the builtins raw_call, create_from_blueprint and create_copy_of can be corrupted. For raw_call, the argument buffer of the call can be corrupted, leading to incorrect calldata in the sub-context. For create_from_blueprint and create_copy_of, the buffer for the to-be-deployed bytecode can be corrupted, leading to deploying incorrect bytecode.
Each builtin has conditions that must be fulfilled for the corruption to happen. For raw_call, the data argument of the builtin must be msg.data and the value or gas passed to the builtin must be some complex expression that results in writing to the memory. For create_copy_of, the value or salt passed to the builtin must be some complex expression that results in writing to the memory. For create_from_blueprint, either no constructor parameters should be passed to the builtin or raw_args should be set to True, and the value or salt passed to the builtin must be some complex expression that results in writing to the memory.
As of time of publication, no patched version exists. The issue is still being investigated, and there might be other cases where the corruption might happen. When the builtin is being called from an internal function F, the issue is not present provided that the function calling F wrote to memory before calling F. As a workaround, the complex expressions that are being passed as kwargs to the builtin should be cached in memory prior to the call to the builtin.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | vyper | ≥ 0.3.4&&< 0.3.10 | 0.3.10 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for vyper. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update vyper to 0.3.10 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-42443 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2023-42443 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2023-42443. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-42443 in your dependencies?
O3 detects CVE-2023-42443 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.