Http4s Ember HTTP/2 does not enforce SETTINGS_MAX_CONCURRENT_STREAMS

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-69203: 0.63% estimated exploitation activity in the next 30 days; percentile 50.24 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

An ember server with HTTP/2 enabled (.withHttp2) does not enforce SETTINGSMAXCONCURRENTSTREAMS 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 PUSHPROMISE 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.

Published by the source

15 Sep 2026, 19:53 UTC

Last modified by the source

15 Sep 2026, 20:00 UTC

Source last checked

26 Oct 2026, 16:55 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-9vwc-pc8p-253q

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-9vwc-pc8p-253q

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# Patch Next advisory brief: CVE-2026-69203

Advisory: Http4s Ember HTTP/2 does not enforce SETTINGS_MAX_CONCURRENT_STREAMS
IDs: CVE-2026-69203, GHSA-9vwc-pc8p-253q
Record: https://patchnext.com/advisories/cve-2026-69203 (revision 2, source checked 26 Oct 2026, 16:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.http4s:http4s-ember-core_2.12 0.23.35; org.http4s:http4s-ember-core_3 1.0.0-M47, 0.23.35; org.http4s:http4s-ember-core_2.13 1.0.0-M47, 0.23.35. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.http4s:http4s-ember-core_2.12: affected <= 0.23.34; fixed in 0.23.35
- Maven org.http4s:http4s-ember-core_3: affected <= 0.23.34; >= 1.0.0-M1, <= 1.0.0-M46; fixed in 0.23.35, 1.0.0-M47
- Maven org.http4s:http4s-ember-core_2.13: affected <= 0.23.34; >= 1.0.0-M1, <= 1.0.0-M46; fixed in 0.23.35, 1.0.0-M47

## Suggested inspection (read-only)
- Maven org.http4s:http4s-ember-core_2.12: check the installed version with your package manager.
- Maven org.http4s:http4s-ember-core_3: check the installed version with your package manager.
- Maven org.http4s:http4s-ember-core_2.13: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.http4s:http4s-ember-core_2.12, org.http4s:http4s-ember-core_3, org.http4s:http4s-ember-core_2.13.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-9vwc-pc8p-253q (OSV record GHSA-9vwc-pc8p-253q lists affected ranges: Maven org.http4s:http4s-ember-core_2.12 >=0 =0 =1.0.0-M1 =0 =1.0.0-M1 <1.0.0-M47 (fixed))
- Verified: https://github.com/advisories/GHSA-9vwc-pc8p-253q (GitHub-reviewed advisory GHSA-9vwc-pc8p-253q lists affected ranges: Maven org.http4s:http4s-ember-core_2.12 >=0 =0 =1.0.0-M1 =0 =1.0.0-M1 <=1.0.0-M46)

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