{"id":"GHSA-9vwc-pc8p-253q","summary":"Http4s Ember HTTP/2 does not enforce SETTINGS_MAX_CONCURRENT_STREAMS","details":"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.\n\n## Impact\n\nUnauthenticated 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).\n\nThe 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.\n\n## Preconditions\n\n- Server: with `.withHttp2` enabled.\n- Client: makes HTTP/2 requests to malicious or compromised sites.  `enablePush` is not enforced.\n\n## Workarounds\n\n- Disable HTTP/2 on `EmberServerBuilder` or `EmberClientBuilder` (default)\n- Client only: avoid HTTP/2 to untrusted servers until patched.","aliases":["CVE-2026-69203"],"modified":"2026-09-15T20:00:40.544947819Z","published":"2026-09-15T19:53:14Z","database_specific":{"nvd_published_at":null,"cwe_ids":["CWE-400","CWE-770"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-09-15T19:53:14Z"},"references":[{"type":"WEB","url":"https://github.com/http4s/http4s/security/advisories/GHSA-9vwc-pc8p-253q"},{"type":"WEB","url":"https://github.com/http4s/http4s/commit/4983de1f93f2caaa3b9de310cf6a9db32c50d66e"},{"type":"PACKAGE","url":"https://github.com/http4s/http4s"},{"type":"WEB","url":"https://github.com/http4s/http4s/releases/tag/v0.23.35"},{"type":"WEB","url":"https://github.com/http4s/http4s/releases/tag/v1.0.0-M47"}],"affected":[{"package":{"name":"org.http4s:http4s-ember-core_2.12","ecosystem":"Maven","purl":"pkg:maven/org.http4s/http4s-ember-core_2.12"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.23.35"}]}],"versions":["0.10.0-M10","0.21.0","0.21.0-M2","0.21.0-M3","0.21.0-M4","0.21.0-M5","0.21.0-M6","0.21.0-RC1","0.21.0-RC2","0.21.0-RC3","0.21.0-RC4","0.21.0-RC5","0.21.1","0.21.11","0.21.12","0.21.13","0.21.14","0.21.15","0.21.16","0.21.17","0.21.18","0.21.19","0.21.2","0.21.20","0.21.21","0.21.22","0.21.23","0.21.24","0.21.25","0.21.26","0.21.27","0.21.28","0.21.29","0.21.3","0.21.30","0.21.31","0.21.32","0.21.33","0.21.34","0.21.4","0.21.5","0.21.6","0.21.7","0.21.8","0.21.9","0.22-129-24d065b","0.22-143-49b5a8d","0.22-53-01128f5","0.22-96-55d3184","0.22.0","0.22.0-M1","0.22.0-M2","0.22.0-M3","0.22.0-M4","0.22.0-M5","0.22.0-M6","0.22.0-M7","0.22.0-M8","0.22.0-RC1","0.22.1","0.22.10","0.22.11","0.22.12","0.22.13","0.22.14","0.22.15","0.22.2","0.22.3","0.22.4","0.22.5","0.22.6","0.22.7","0.22.8","0.22.9","0.23.0","0.23.0-M1","0.23.0-RC1","0.23.1","0.23.10","0.23.11","0.23.12","0.23.13","0.23.14","0.23.15","0.23.16","0.23.17","0.23.18","0.23.19","0.23.19-RC1","0.23.19-RC2","0.23.19-RC3","0.23.2","0.23.20","0.23.21","0.23.22","0.23.23","0.23.24","0.23.25","0.23.26","0.23.27","0.23.28","0.23.29","0.23.3","0.23.30","0.23.31","0.23.32","0.23.33","0.23.34","0.23.4","0.23.5","0.23.6","0.23.7","0.23.8","0.23.9"],"database_specific":{"last_known_affected_version_range":"\u003c= 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