CVE-2023-39363 — vyper
Fix: vyperlang/vyper#2439CVE-2023-39363 is a CWE-863 vulnerability in vyper. 3 public exploit references exist, so weaponization risk is real. A fix is available for vyper — see the affected versions and patch details below.
Vyper incorrectly allocated named re-entrancy locks
Exploitation Status
No confirmed exploitation observed yet
- 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-2023-39363.
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.
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
In versions 0.2.15, 0.2.16 and 0.3.0, named re-entrancy locks are allocated incorrectly. Each function using a named re-entrancy lock gets a unique lock regardless of the key, allowing cross-function re-entrancy in contracts compiled with the susceptible versions. A specific set of conditions is required to result in misbehavior of affected contracts, specifically:
- A
.vycontract compiled with either of the followingvyperversions:0.2.15,0.2.16,0.3.0 - A primary function that utilizes the
@nonreentrantdecorator with a specifickeyand does not strictly follow the check-effects-interaction pattern (i.e. contains an external call to an untrusted party before storage updates) - A secondary function that utilizes the same
keyand would be affected by the improper state caused by the primary function
Patches
https://github.com/vyperlang/vyper/pull/2439, https://github.com/vyperlang/vyper/pull/2514
Workarounds
Upgrade to 0.3.1 or higher
References
Technical post-mortem report: https://hackmd.io/@vyperlang/HJUgNMhs2
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | vyper | ≥ 0.2.15&&< 0.3.1 | 0.3.1pip install --upgrade 'vyper==0.3.1' |
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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update vyper to 0.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-39363 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-39363 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-39363. 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-2023-39363 in your dependencies?
O3 Security finds CVE-2023-39363 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.