CVE-2026-69205 is a high-severity (CVSS 8.7) CWE-444 vulnerability in org.http4s:http4s-ember-core_3. O3 Security confirms whether CVE-2026-69205 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Http4s Ember Transfer-Encoding value parsing (TE.CL / TE.0 request smuggling)
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-69205.
Real-World Exposure
org.http4s:http4s-ember-core_3☕org.http4s:http4s-ember-core_2.13☕org.http4s:http4s-ember-core_2.12☕org.http4s:http4s-ember-core_2.13☕org.http4s:http4s-ember-core_3Real-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
Ember's HTTP/1.1 header parser matches the Transfer-Encoding header value
with a case-sensitive substring test (hValue.contains("chunked")). RFC
9112 §7 requires transfer-coding names to be compared case-insensitively. A
request carrying Transfer-Encoding: Chunked (capital C) is therefore not
recognised as chunked, and Ember falls back to framing by Content-Length
(or zero if absent) while a compliant intermediary frames the same bytes by
chunked encoding. The two parsers then disagree on where the request body
ends, enabling HTTP request smuggling (TE.CL / TE.0).
The same line of code admits two further variants:
- The substring test misfires on
Transfer-Encoding: notchunked(an inverse desync — Ember treats it as chunked while a compliant intermediary rejects the unknown coding). - Header field bytes are decoded with the platform-default charset. Under
UTF-8 the wire bytes
E2 84 AAdecode to U+212A KELVIN SIGN, whichString.equalsIgnoreCaseUnicode-case-folds tok, soTransfer-Encoding: chun<U+212A>edmatcheschunkedonce the comparison is made case-insensitive without also pinning the decode to ISO-8859-1.
Impact
Server
Request smuggling when ember-server is an origin behind an intermediary that
honours Transfer-Encoding case-insensitively per RFC, forwards the header
value verbatim, and reuses keep-alive connections to the backend:
- Front-end security bypass: the smuggled request reaches paths the intermediary's ACL/auth layer would have blocked, with attacker-chosen method and headers.
- Cross-user request hijack: a partial smuggled prefix left in Ember's
connection buffer is concatenated with the next victim's request on the
same pooled backend connection, exposing its headers (e.g.
Cookie,Authorization) to the attacker. - Cache poisoning: the smuggled response is associated with the next request key in a caching proxy.
Client
ember-client shares the same HeaderP.parse on the response path, enabling
response smuggling when http4s is used as a gateway. This is less severe: it
requires a malicious or compromised upstream rather than an anonymous remote
client.
Preconditions
- Unauthenticated remote attacker (server)
- ember-server as origin behind a keep-alive intermediary
- Intermediary treats
Transfer-Encodingcase-insensitively (per RFC) and forwards the header value without lowercasing it - Malicious or compromised upstream (client)
Workarounds
- Intermediary fully buffers and re-encodes request bodies (e.g. nginx with
default
proxy_request_buffering on) - Intermediary normalises the
Transfer-Encodingvalue (lowercases the token) before forwarding - Disable backend keep-alive between the intermediary and Ember
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.http4s:http4s-ember-core_3 | all versions | 0.23.35 |
| ☕Maven | org.http4s:http4s-ember-core_2.13 | all versions | 0.23.35 |
| ☕Maven | org.http4s:http4s-ember-core_2.12 | all versions | 0.23.35 |
| ☕Maven | org.http4s:http4s-ember-core_2.13 | ≥ 1.0.0-M1&&< 1.0.0-M47 | 1.0.0-M47 |
| ☕Maven | org.http4s:http4s-ember-core_3 | ≥ 1.0.0-M1&&< 1.0.0-M47 | 1.0.0-M47 |
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-ember-core_3. 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-ember-core_3 to 0.23.35 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-69205 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-2026-69205 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-2026-69205. 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-2026-69205 in your dependencies?
O3 detects CVE-2026-69205 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.