How severe is CVE-2026-69203?

CVE-2026-69203 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-69203?

CVE-2026-69203 affects the following packages: org.http4s:http4s-ember-core_2.12 (Maven), org.http4s:http4s-ember-core_2.13 (Maven), org.http4s:http4s-ember-core_3 (Maven), org.http4s:http4s-ember-core_2.13 (Maven), org.http4s:http4s-ember-core_3 (Maven). Ecosystems affected: Maven.

How do I fix CVE-2026-69203?

Update org.http4s:http4s-ember-core_2.12 to 0.23.35 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-69203 is resolved across your whole dependency graph.

How do I detect CVE-2026-69203 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.http4s:http4s-ember-core_2.12, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-69203 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-69203 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-69203 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-69203?

CVE-2026-69203 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 50th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-69203?

CVE-2026-69203 is classified as Uncontrolled Resource Consumption (CWE-400), CWE-770 (CWE-770). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-69203 published, and has it been updated?

CVE-2026-69203 was published on September 15, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

HIGH severity

CVE-2026-69203 — http4s-ember-core_2.12

HIGHFix: http4s/http4s@4983de1

CVE-2026-69203 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in org.http4s:http4s-ember-core_2.12. A fix is available for org.http4s:http4s-ember-core_2.12 — see the affected versions and patch details below.

Http4s Ember HTTP/2: does not enforce SETTINGS_MAX_CONCURRENT_STREAMS

Also known asGHSA-9vwc-pc8p-253q

Published

Sep 15, 2026

Updated

Oct 28, 2026

Affected

5 pkgs

Patched

5 / 5

Exploits

None indexed

Exploitation data as of Oct 30, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
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-2026-69203.

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs50th percentile — riskier than 50% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-69203 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 398,142 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

5 pkgs affected

☕org.http4s:http4s-ember-core_2.12☕org.http4s:http4s-ember-core_2.13☕org.http4s:http4s-ember-core_3☕org.http4s:http4s-ember-core_2.13☕org.http4s:http4s-ember-core_3

Real-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

An ember server with HTTP/2 enabled (.withHttp2) does not enforce SETTINGS_MAX_CONCURRENT_STREAMS on streams opened by the peer. A single unauthenticated connection can open an unbounded number of concurrent streams, each of which allocates per-stream server state that is never released, exhausting the heap.

Impact

Unauthenticated remote denial of service (memory exhaustion) against any Ember server built .withHttp2. This is the resource-exhaustion class of the HTTP/2 "Rapid Reset" family (CVE-2023-44487).

The same unchecked allocation path is reachable on the client via server-initiated PUSH_PROMISE frames, so a malicious or compromised server can exhaust an ember-client's heap the same way.

Preconditions

Server: with .withHttp2 enabled.
Client: makes HTTP/2 requests to malicious or compromised sites. enablePush is not enforced.

Workarounds

Disable HTTP/2 on EmberServerBuilder or EmberClientBuilder (default)
Client only: avoid HTTP/2 to untrusted servers until patched.

Affected Packages

5 total 5 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.http4s:http4s-ember-core_2.12`	all versions	0.23.35`org.http4s:http4s-ember-core_2.12:0.23.35`
☕Maven	`org.http4s:http4s-ember-core_2.13`	all versions	0.23.35`org.http4s:http4s-ember-core_2.13:0.23.35`
☕Maven	`org.http4s:http4s-ember-core_3`	all versions	0.23.35`org.http4s:http4s-ember-core_3:0.23.35`
☕Maven	`org.http4s:http4s-ember-core_2.13`	≥ 1.0.0-M1&&< 1.0.0-M47	1.0.0-M47`org.http4s:http4s-ember-core_2.13:1.0.0-M47`
☕Maven	`org.http4s:http4s-ember-core_3`	≥ 1.0.0-M1&&< 1.0.0-M47	1.0.0-M47`org.http4s:http4s-ember-core_3:1.0.0-M47`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.http4s:http4s-ember-core_2.12, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.http4s:http4s-ember-core_2.12 to 0.23.35 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-69203 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

An ember server with HTTP/2 enabled (`.withHttp2`) does not enforce `SETTINGS_MAX_CONCURRENT_STREAMS` on streams opened by the peer. A single unauthenticated connection can open an unbounded number of concurrent streams, each of which allocates per-stream server state that is never released, exhausting the heap. ## Impact Unauthenticated remote denial of service (memory exhaustion) against any Ember server built `.withHttp2`. This is the resource-exhaustion class of the HTTP/2 "Rapid Reset" family (CVE-2023-44487). The same unchecked allocation path is reachable on the client via server-i