What’s Vulnerable › Vulnerabilities

CVE-2024-40627: OpaMiddleware does not filter HTTP OPTIONS requests

• Severity: medium (CVSS 5.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-07-15 · updated 2026-06-17
• Weakness: CWE-204

Description

Fastapi OPA is an opensource fastapi middleware which includes auth flow. HTTP `OPTIONS` requests are always allowed by `OpaMiddleware`, even when they lack authentication, and are passed through directly to the application. `OpaMiddleware` allows all HTTP `OPTIONS` requests without evaluating it against any policy. If an application provides different responses to HTTP `OPTIONS` requests based on an entity existing (such as to indicate whether an entity is writable on a system level), an unauthenticated attacker could discover which entities exist within an application. This issue has been addressed in release version 2.0.1. All users are advised to upgrade. There are no known workarounds for this vulnerability.

Affected products

• busykoala fastapi-opa: before 2.0.1 — fixed in 2.0.1

How to fix

Upgrade to a fixed version: busykoala fastapi-opa 2.0.1. Check the vendor advisory for mitigations.

References

• https://github.com/busykoala/fastapi-opa/blob/6dd6f8c87e908fe080784a74707f016f1422b58a/fastapi_opa/opa/opa_middleware.py#L79-L80
• https://github.com/busykoala/fastapi-opa/commit/9588109ff651f7ffc92687129c4956126443fb8c
• https://github.com/busykoala/fastapi-opa/security/advisories/GHSA-5f5c-8rvc-j8wf
• https://github.com/busykoala/fastapi-opa/blob/6dd6f8c87e908fe080784a74707f016f1422b58a/fastapi_opa/opa/opa_middleware.py#L79-L80
• https://github.com/busykoala/fastapi-opa/commit/9588109ff651f7ffc92687129c4956126443fb8c
• https://github.com/busykoala/fastapi-opa/security/advisories/GHSA-5f5c-8rvc-j8wf

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