Summary
Http4s Ember HTTP/2 has an unbounded outbound frame queue
Ember's HTTP/2 connection serializes all outgoing frames through a single unbounded queue drained by one writer fiber (writeLoop). When the write side stalls, any frames the connection keeps producing accumulate in that queue without limit. The peer can drive this cheaply because the connection emits a control frame in response to inbound frames it does not flow-control: one PING ACK per PING, one SETTINGS ACK per SETTINGS, and a WINDOW_UPDATE per inbound DATA. A single unauthenticated connection can therefore exhaust heap and OOM the process.
This affects an ember server (malicious client) and an ember client (malicious/compromised server that floods the client and stops reading its ACKs).
Preconditions
- Ember server or client built
.withHttp2, speaking to a hostile or compromised peer.
Workarounds
- Disable HTTP/2 (do not call
.withHttp2).
Impact
Unauthenticated remote denial of service (OOM) against any ember server built .withHttp2, from a single connection, at negligible attacker cost (tiny control frames). Also affects an ember client talking to a hostile HTTP/2 server.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2026-69213 has a CVSS score of 7.5 (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
Security releases
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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See it in your environmentNew to Kodem? Get a demo →Remediation advice
org.http4s:http4s-ember-core_2.12 to 0.23.35 or later; org.http4s:http4s-ember-core_2.13 to 0.23.35 or later; org.http4s:http4s-ember-core_3 to 0.23.35 or later; org.http4s:http4s-ember-core_3 to 1.0.0-M47 or later; org.http4s:http4s-ember-core_2.13 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
- What is CVE-2026-69213? CVE-2026-69213 is a high-severity uncontrolled resource consumption vulnerability in org.http4s:http4s-ember-core_2.12 (maven), affecting versions <= 0.23.34. It is fixed in 0.23.35, 1.0.0-M47. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2026-69213? CVE-2026-69213 has a CVSS score of 7.5 (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.
- Which packages are affected by CVE-2026-69213?
org.http4s:http4s-ember-core_2.12(maven) (versions <= 0.23.34)org.http4s:http4s-ember-core_2.13(maven) (versions <= 0.23.34)org.http4s:http4s-ember-core_3(maven) (versions <= 0.23.34)
- Is there a fix for CVE-2026-69213? Yes. CVE-2026-69213 is fixed in 0.23.35, 1.0.0-M47. Upgrade to this version or later.
- Is CVE-2026-69213 exploitable, and should I be worried? Whether CVE-2026-69213 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
- What actually determines whether CVE-2026-69213 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.
- How do I fix CVE-2026-69213?
- Upgrade
org.http4s:http4s-ember-core_2.12to 0.23.35 or later - Upgrade
org.http4s:http4s-ember-core_2.13to 0.23.35 or later - Upgrade
org.http4s:http4s-ember-core_3to 0.23.35 or later - Upgrade
org.http4s:http4s-ember-core_3to 1.0.0-M47 or later - Upgrade
org.http4s:http4s-ember-core_2.13to 1.0.0-M47 or later
- Upgrade