CVE-2026-73494 is a high-severity (CVSS 7.4) vulnerability in org.http4s:http4s-blaze-server_2.13. O3 Security confirms whether CVE-2026-73494 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
blaze: Multiple HTTP/1.1 request-smuggling primitives in blaze's Java wire parser
Real-World Exposure
org.http4s:http4s-blaze-server_2.13☕org.http4s:blaze-http_2.13☕org.http4s:blaze-http_3☕org.http4s:blaze-http_3☕org.http4s:blaze-http_2.13Real-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
Summary
Five independent HTTP/1.1 conformance laxities in blaze's hand-written Java parser (http/src/main/java/org/http4s/blaze/http/parser/) cause request-boundary disagreement with a stricter intermediary. All are reachable from a default BlazeServerBuilder with no non-default configuration.
Impact
Actual exploitability depends on the fronting proxy — a boundary disagreement requires a pair of parsers that disagree. Where the proxy forwards the malformed bytes and derives a different message boundary, the consequences are the standard set: front-end ACL/auth bypass, response-queue poisoning on pooled backend connections, and cache poisoning. Risk concentrates on lenient or legacy intermediaries.
Workarounds
Deploy behind an RFC-strict reverse proxy (nginx, HAProxy, Envoy, ALB) that rejects or re-serializes malformed requests at the edge; this neutralizes most of these for deployments that cannot upgrade immediately.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.http4s:http4s-blaze-server_2.13 | all versions | 0.23.18 |
| ☕Maven | org.http4s:blaze-http_2.13 | all versions | 0.23.18 |
| ☕Maven | org.http4s:blaze-http_3 | all versions | 0.23.18 |
| ☕Maven | org.http4s:blaze-http_3 | ≥ 1.0.0-M1&&< 1.0.0-M42 | 1.0.0-M42 |
| ☕Maven | org.http4s:blaze-http_2.13 | ≥ 1.0.0-M1&&< 1.0.0-M42 | 1.0.0-M42 |
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-blaze-server_2.13. 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-blaze-server_2.13 to 0.23.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-73494 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 CVE-2026-73494 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-2026-73494. 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-2026-73494 in your dependencies?
O3 detects CVE-2026-73494 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.