GHSA-crq5-92j2-j7wv
Http4s: ResourceService and Webjar Service path escape via percent-encoded separators
Packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| Maven | org.http4s:http4s-server_2.12 | < 0.23.35 | 0.23.35 |
| Maven | org.http4s:http4s-server_2.13 | < 0.23.35 | 0.23.35 |
| Maven | org.http4s:http4s-server_3 | < 0.23.35 | 0.23.35 |
| Maven | org.http4s:http4s-server_3 | >= 1.0.0-M1, < 1.0.0-M47 | 1.0.0-M47 |
| Maven | org.http4s:http4s-server_2.13 | >= 1.0.0-M1, < 1.0.0-M47 | 1.0.0-M47 |
Details
As written in the advisory (Markdown source, shown as plain text).
The static content handlers `ResourceService` and `WebjarService` URL decode each path segment and then reject only segments that are exactly `""`, `"."`, or `".."`. A percent-encoded separator (`%2F`) lets an attacker smuggle a `../` segment past that filter and escape the configured base, reading resources that should not be public.
On Windows, a similar attack exists with (`%5C`).
## Impact
Disclosure of classpath or webjar resources outside the configured base.
## Preconditions
- Application uses `ResourceService` (with a non-root base path) or `WebjarService`
- At least one classpath entry is served from a directory (e.g. `sbt run`, exploded .war)
- Backend forwards `%2F`/`%5C` without normalizing (e.g., Ember, Blaze)
## Fixes
The patch rejects any decoded path segment containing `/` (`%2F`) or `\` (`%5C`) with a `400 Bad Request` in `ResourceService` and `WebjarService`.
`FileService` was not exploitable, but the same guards are applied for consistency and to remove its reliance on path normalization.
## Workarounds
- Deploy as a fat jar, with no filesystem directories on the classpath.
- Front the service with a proxy that rejects/normalizes `%2F` and `%5C` in the request path.
References
External links from the advisory. They lead to third-party sites.