CVE-2021-32643: StaticFile.fromUrl can leak presence of a directory

Severity: medium (CVSS 5.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-05-27 · updated 2026-06-17
Weakness: CWE-22

Description

Http4s is a Scala interface for HTTP services. `StaticFile.fromUrl` can leak the presence of a directory on a server when the `URL` scheme is not `file://`, and the URL points to a fetchable resource under its scheme and authority. The function returns `F[None]`, indicating no resource, if `url.getFile` is a directory, without first checking the scheme or authority of the URL. If a URL connection to the scheme and URL would return a stream, and the path in the URL exists as a directory on the server, the presence of the directory on the server could be inferred from the 404 response. The contents and other metadata about the directory are not exposed. This affects http4s versions: 0.21.7 through 0.21.23, 0.22.0-M1 through 0.22.0-M8, 0.23.0-M1, and 1.0.0-M1 through 1.0.0-M22. The [patch](https://github.com/http4s/http4s/commit/52e1890665410b4385e37b96bc49c5e3c708e4e9) is available in the following versions: v0.21.24, v0.22.0-M9, v0.23.0-M2, v1.0.0-M23. As a workaround users can avoid calling `StaticFile.fromUrl` with non-file URLs.

Affected products

http4s: from 0.21.7 before 0.21.24; 0.22.0-milestone1, 0.22.0-milestone2, 0.22.0-milestone3, 0.22.0-milestone4, 0.22.0-milestone5, 0.22.0-milestone6 (+25) — fixed in 0.21.24

How to fix

Upgrade to a fixed version: http4s 0.21.24. Check the vendor advisory for mitigations.

References

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