CVE-2026-69205

CVE-2026-69205 is a high-severity security vulnerability in org.http4s:http4s-ember-core_3 (maven), affecting versions <= 0.23.34. It is fixed in 0.23.35, 1.0.0-M47.

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Summary

Http4s Ember Transfer-Encoding value parsing (TE.CL / TE.0 request smuggling)

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 AA decode to U+212A KELVIN SIGN, which
    String.equalsIgnoreCase Unicode-case-folds to k, so
    Transfer-Encoding: chun<U+212A>ed matches chunked once the comparison
    is made case-insensitive without also pinning the decode to ISO-8859-1.

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-Encoding case-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-Encoding value (lowercases the
    token) before forwarding
  • Disable backend keep-alive between the intermediary and Ember

Impact

CVE-2026-69205 has a CVSS score of 8.7 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.23.35, 1.0.0-M47); upgrading removes the vulnerable code path.

Affected versions

org.http4s:http4s-ember-core_3 (<= 0.23.34) org.http4s:http4s-ember-core_2.13 (<= 0.23.34) org.http4s:http4s-ember-core_2.12 (<= 0.23.34) org.http4s:http4s-ember-core_2.13 (>= 1.0.0-M1, <= 1.0.0-M46) org.http4s:http4s-ember-core_3 (>= 1.0.0-M1, <= 1.0.0-M46)

Security releases

org.http4s:http4s-ember-core_3 → 0.23.35 (maven) org.http4s:http4s-ember-core_2.13 → 0.23.35 (maven) org.http4s:http4s-ember-core_2.12 → 0.23.35 (maven) org.http4s:http4s-ember-core_2.13 → 1.0.0-M47 (maven) org.http4s:http4s-ember-core_3 → 1.0.0-M47 (maven)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

Upgrade the following packages to resolve this vulnerability:

org.http4s:http4s-ember-core_3 to 0.23.35 or later; org.http4s:http4s-ember-core_2.13 to 0.23.35 or later; org.http4s:http4s-ember-core_2.12 to 0.23.35 or later; org.http4s:http4s-ember-core_2.13 to 1.0.0-M47 or later; org.http4s:http4s-ember-core_3 to 1.0.0-M47 or later

Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.

Frequently Asked Questions

  1. What is CVE-2026-69205? CVE-2026-69205 is a high-severity security vulnerability in org.http4s:http4s-ember-core_3 (maven), affecting versions <= 0.23.34. It is fixed in 0.23.35, 1.0.0-M47.
  2. How severe is CVE-2026-69205? CVE-2026-69205 has a CVSS score of 8.7 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
  3. Which packages are affected by CVE-2026-69205?
    • org.http4s:http4s-ember-core_3 (maven) (versions <= 0.23.34)
    • org.http4s:http4s-ember-core_2.13 (maven) (versions <= 0.23.34)
    • org.http4s:http4s-ember-core_2.12 (maven) (versions <= 0.23.34)
  4. Is there a fix for CVE-2026-69205? Yes. CVE-2026-69205 is fixed in 0.23.35, 1.0.0-M47. Upgrade to this version or later.
  5. Is CVE-2026-69205 exploitable, and should I be worried? Whether CVE-2026-69205 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
  6. What actually determines whether CVE-2026-69205 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
  7. How do I fix CVE-2026-69205?
    • Upgrade org.http4s:http4s-ember-core_3 to 0.23.35 or later
    • Upgrade org.http4s:http4s-ember-core_2.13 to 0.23.35 or later
    • Upgrade org.http4s:http4s-ember-core_2.12 to 0.23.35 or later
    • Upgrade org.http4s:http4s-ember-core_2.13 to 1.0.0-M47 or later
    • Upgrade org.http4s:http4s-ember-core_3 to 1.0.0-M47 or later

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