CVE-2021-39185
CRITICALCVE-2021-39185 is a critical-severity (CVSS 9.1) CWE-346 vulnerability in org.http4s:http4s-server_2.13.0-M5. O3 Security confirms whether CVE-2021-39185 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Default CORS config allows any origin with credentials
Real-World Exposure
org.http4s:http4s-server_2.13.0-M5☕org.http4s:http4s-server_3☕org.http4s:http4s-server_3☕org.http4s:http4s-server_2.10☕org.http4s:http4s-server_2.11☕org.http4s:http4s-server_2.12☕org.http4s:http4s-server_2.12☕org.http4s:http4s-server_2.12+3 moreReal-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
Http4s is a minimal, idiomatic Scala interface for HTTP services. In http4s versions 0.21.26 and prior, 0.22.0 through 0.22.2, 0.23.0, 0.23.1, and 1.0.0-M1 through 1.0.0-M24, the default CORS configuration is vulnerable to an origin reflection attack. The middleware is also susceptible to a Null Origin Attack. The problem is fixed in 0.21.27, 0.22.3, 0.23.2, and 1.0.0-M25. The original CORS implementation and CORSConfig are deprecated. See the GitHub GHSA for more information, including code examples and workarounds.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.http4s:http4s-server_2.13.0-M5 | all versions | No fix |
| ☕Maven | org.http4s:http4s-server_3 | ≥ 0.22.0&&< 0.22.3 | 0.22.3 |
| ☕Maven | org.http4s:http4s-server_3 | ≥ 0.23.0&&< 0.23.2 | 0.23.2 |
| ☕Maven | org.http4s:http4s-server_2.10 | all versions | No fix |
| ☕Maven | org.http4s:http4s-server_2.11 | all versions | No fix |
| ☕Maven | org.http4s:http4s-server_2.12 | all versions | 0.21.27 |
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_2.13.0-M5. 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
No patched version of org.http4s:http4s-server_2.13.0-M5 has shipped for CVE-2021-39185 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
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 CVE-2021-39185 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 CVE-2021-39185. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-39185 in your dependencies?
O3 detects CVE-2021-39185 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.