CVE-2023-31146 is a high-severity (CVSS 7.5) Out-of-bounds Write vulnerability in vyper. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for vyper — see the affected versions and patch details below.
Vyper vulnerable to OOB DynArray access when array is on both LHS and RHS of an assignment
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-31146.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
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
Impact
during codegen, the length word of a dynarray is written before the data, which can result in OOB array access in the case where the dynarray is on both the lhs and rhs of an assignment. here is a minimal example producing the issue:
a:DynArray[uint256,3]
@external
def test() -> DynArray[uint256,3]:
self.a = [1,2,3]
self.a = empty(DynArray[uint256,3])
self.a = [self.a[0],self.a[1],self.a[2]]
return self.a # return [1,2,3]
and here is an example demonstrating the issue can cause data corruption across call frames:
@external
def test() -> DynArray[uint256,3]:
self.a()
return self.b() # return [1,2,3]
@internal
def a():
a: uint256 = 0
b: uint256 = 1
c: uint256 = 2
d: uint256 = 3
@internal
def b() -> DynArray[uint256,3]:
a: DynArray[uint256,3] = empty(DynArray[uint256,3])
a = [a[0],a[1],a[2]]
return a
examples involving append and pop:
@internal
def foo():
c: DynArray[uint256, 1] = []
c.append(c[0])
@internal
def foo():
c: DynArray[uint256, 1] = [1]
c[0] = c.pop()
the expected behavior in all of the above cases is to revert due to oob array access.
Patches
patched in 4f8289a81206f767df1900ac48f485d90fc87edb
Workarounds
Is there a way for users to fix or remediate the vulnerability without upgrading?
References
Are there any links users can visit to find out more?
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | vyper | all versions | 0.3.8pip install --upgrade 'vyper==0.3.8' |
Affected Products
vypervyperlangResearch 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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update vyper to 0.3.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-31146 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.
Frequently Asked Questions
Is CVE-2023-31146 in your dependencies?
Find it across PyPI, including transitive dependencies.