Summary
Vyper has incorrectly allocated named re-entrancy locks
Workarounds
Upgrade to 0.3.1 or higher
References
Technical post-mortem report: https://hackmd.io/@vyperlang/HJUgNMhs2
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
The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.
CVE-2023-39363 has a CVSS score of 8.7 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.3.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2023-39363? CVE-2023-39363 is a critical-severity incorrect authorization vulnerability in vyper (pip), affecting versions >= 0.2.15, < 0.3.1. It is fixed in 0.3.1. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
- How severe is CVE-2023-39363? CVE-2023-39363 has a CVSS score of 8.7 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of vyper are affected by CVE-2023-39363? vyper (pip) versions >= 0.2.15, < 0.3.1 is affected.
- Is there a fix for CVE-2023-39363? Yes. CVE-2023-39363 is fixed in 0.3.1. Upgrade to this version or later.
- Is CVE-2023-39363 exploitable, and should I be worried? Whether CVE-2023-39363 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2023-39363 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2023-39363? Upgrade
vyperto 0.3.1 or later.