GHSA-66q9-f7ff-mmx6 is a high-severity (CVSS 7.6) CWE-23 vulnerability in org.http4s:http4s-server_2.12. O3 Security confirms whether GHSA-66q9-f7ff-mmx6 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Local file inclusion vulnerability in http4s
Real-World Exposure
org.http4s:http4s-server_2.12☕org.http4s:http4s-server_2.12☕org.http4s:http4s-server_2.12Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Impact
This vulnerability applies to all users of:
org.http4s.server.staticcontent.FileServiceorg.http4s.server.staticcontent.ResourceServiceorg.http4s.server.staticcontent.WebjarService
Path escaping
URI normalization is applied incorrectly. Requests whose path info contain ../ or // can expose resources outside of the configured location. Specifically:
FileServicemay expose any file on the local file system.ResourceServicemay expose any resource on the class path.
Prefix matching
When the service is configured with a non-empty pathPrefix that doesn't end in a slash, any directories whose names are a prefix of systemPath (from FileService) or pathPrefix (from ResourceService) are exposed. For example, if pathPrefix is /foo and systemPath is /bar, a request to /foobaz/quux.txt exposes file /barbaz/quux.txt, when only files beneath /bar should be available.
URI decoding
URI segments are not decoded before resource resolution. This causes resources with reserved characters in their name to incorrectly return a 404. It also may incorrectly expose the rare resource whose name is URI encoded. This applies to FileService, ResourceService, and WebjarService.
Patches
In all three services, paths with an empty segment, a . segment, or a .. segment are now rejected with a 400 Bad Request response. This fixes exposure outside the configured root. Many clients already eliminate dot segments according to the rules in RFC3986, Section 5.2.4. A middleware that does so at the server level may be considered if there is demand.
If pathInfo is non-empty, and does not begin with /, then a 404 response is generated. This fixes the prefix matching exposure.
All path segments are URI decoded before being passed to the file system or resource path. This allows resolution of resources with reserved characters in the name, and prevents incorrect exposure of resources whose names are themselves URI encoded.
Workarounds
The recommended course is to upgrade:
- v0.18.26, binary compatible with the 0.18.x series
- v0.20.20, binary compatible with the 0.20.x series
- v0.21.2, binary compatible with the 0.21.x series
Note that 0.19.0 is a deprecated release and has never been supported.
If an upgrade is impossible:
- Temporarily copy
FileService.scala,ResourceService.scala, andWebjarService.scalafrom the appropriate release series into your project and recompile with that, changing the package name and reference in your application. - Users of a servlet backend can use the servlet container's file serving capabilities.
Credits
Thank you to Thomas Gøytil for the discovery, responsible disclosure, and assistance testing of this vulnerability.
For more information
If you have any questions or comments about this advisory:
- Open an issue in http4s/http4s
- Email a maintainer:
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.http4s:http4s-server_2.12 | all versions | 0.18.26 |
| ☕Maven | org.http4s:http4s-server_2.12 | ≥ 0.19.0&&< 0.20.20 | 0.20.20 |
| ☕Maven | org.http4s:http4s-server_2.12 | ≥ 0.21.0&&< 0.21.2 | 0.21.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.http4s:http4s-server_2.12. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update org.http4s:http4s-server_2.12 to 0.18.26 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-66q9-f7ff-mmx6 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-66q9-f7ff-mmx6 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-66q9-f7ff-mmx6. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-66q9-f7ff-mmx6 in your dependencies?
O3 detects GHSA-66q9-f7ff-mmx6 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.