How severe is CVE-2023-39363?

No CVSS score has been assigned to CVE-2023-39363 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2023-39363?

CVE-2023-39363 affects the following packages: vyper (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2023-39363?

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.

How do I detect CVE-2023-39363 in my PyPI dependencies?

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.

How do I mitigate CVE-2023-39363 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2023-39363 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2023-39363, including 3 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2023-39363?

CVE-2023-39363 has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 58th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2023-39363?

CVE-2023-39363 is classified as CWE-863 (CWE-863). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2023-39363 published, and has it been updated?

CVE-2023-39363 was published on August 7, 2023 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

CVE-2023-39363 — vyper

Fix: vyperlang/vyper#2439

CVE-2023-39363 is a CWE-863 vulnerability in vyper. 3 public exploit or proof-of-concept references are indexed, 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

Also known asGHSA-5824-cm3x-3c38PYSEC-2023-142

Published

Aug 7, 2023

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

3 known

Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs58th percentile — riskier than 58% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍vyper

Real-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 .vy contract compiled with either of the following vyper versions: 0.2.15, 0.2.16, 0.3.0
A primary function that utilizes the @nonreentrant decorator with a specific key and 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 key and 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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`vyper`	≥ 0.2.15&&< 0.3.1	0.3.1`pip install --upgrade 'vyper==0.3.1'`

Affected Products

1 product · 3 configurations

Application

vypervyperlang

3 versions

0.2.150.2.160.3.0

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Mac…

github.comNVDAug 2023

Report on hackmd.io

hackmd.ioNVDAug 2023

Report on hackmd.io

hackmd.ioNVDAug 2023

Detection & mitigation playbook

Open-source dependency

Detect
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
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### 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 `.vy` contract compiled with either of the following `vyper` versions: `0.2.15`, `0.2.16`, `0.3.0` - A primary function that utilizes the `@nonreentrant` decorator with a specific `key` and does not strictly follow

O3 Security · Impact-Aware SCA

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