GHSA-CP4Q-FQW9-4HF6
Vulnerability from github – Published: 2026-09-15 20:01 – Updated: 2026-09-15 20:01When Ember receives an HTTP/2 HEADERS or PUSH_PROMISE frame without the END_HEADERS flag, it buffers the header block fragment and waits for subsequent CONTINUATION frames. These accumulate unbounded until the connection closes.
Impact
A remote, unauthenticated peer can exhaust the heap on any Ember endpoint that has HTTP/2 enabled:
- ember-server with
.withHttp2: any HTTP/2 client can trigger this against any reachable path (including paths that return 404). No authentication is required because the attack completes before the request is decoded. - ember-client with
.withHttp2: a malicious or compromised origin server can trigger this via the response header block. A single in-flight request is sufficient.
Memory consumption is bounded only by the attacker's upload bandwidth and the connection lifetime.
Prerequisites
EmberServerBuilderconfigured with.withHttp2.- For the server: the attacker can establish an HTTP/2 connection
- For the client: the application makes a request to an attacker-controlled origin. HTTP/2 incoming headers exceeding the configured size limit are buffer in order to generate an informative HTTP 413 response. If a client does not stop sending headers, this leads to memory exhaustion.
Patches
The fix bounds the accumulated header-block size at SETTINGS_MAX_HEADER_LIST_SIZE (derived from EmberServerBuilder.maxHeaderSize / EmberClientBuilder.maxResponseHeaderSize). When a CONTINUATION frame would push the accumulated block over that limit, the connection is terminated with GOAWAY. The receiveHeadersTimeout additionally bounds how long an incomplete header block may remain open.
Workarounds
- Disable HTTP/2 (
.withHttp2) until upgraded (default). It is off by default. - If HTTP/2 must remain enabled, place ember behind a reverse proxy that terminates HTTP/2 and speaks HTTP/1.1 to ember.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 0.23.34"
},
"package": {
"ecosystem": "Maven",
"name": "org.http4s:http4s-ember-core_2.12"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.23.35"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 0.23.34"
},
"package": {
"ecosystem": "Maven",
"name": "org.http4s:http4s-ember-core_2.13"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.23.35"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 0.23.34"
},
"package": {
"ecosystem": "Maven",
"name": "org.http4s:http4s-ember-core_3"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.23.35"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 1.0.0-M46"
},
"package": {
"ecosystem": "Maven",
"name": "org.http4s:http4s-ember-core_2.13"
},
"ranges": [
{
"events": [
{
"introduced": "1.0.0-M1"
},
{
"fixed": "1.0.0-M47"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 1.0.0-M46"
},
"package": {
"ecosystem": "Maven",
"name": "org.http4s:http4s-ember-core_3"
},
"ranges": [
{
"events": [
{
"introduced": "1.0.0-M1"
},
{
"fixed": "1.0.0-M47"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-69218"
],
"database_specific": {
"cwe_ids": [
"CWE-770"
],
"github_reviewed": true,
"github_reviewed_at": "2026-09-15T20:01:08Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "When Ember receives an HTTP/2 `HEADERS` or `PUSH_PROMISE` frame without the `END_HEADERS` flag, it buffers the header block fragment and waits for subsequent `CONTINUATION` frames. These accumulate unbounded until the connection closes. \n\n### Impact\n\nA remote, unauthenticated peer can exhaust the heap on any Ember endpoint that has HTTP/2 enabled:\n\n- **ember-server with `.withHttp2`**: any HTTP/2 client can trigger this against any reachable path (including paths that return 404). No authentication is required because the attack completes before the request is decoded.\n- **ember-client with `.withHttp2`**: a malicious or compromised origin server can trigger this via the response header block. A single in-flight request is sufficient.\n\nMemory consumption is bounded only by the attacker\u0027s upload bandwidth and the connection lifetime.\n\n### Prerequisites\n\n- `EmberServerBuilder` configured with `.withHttp2`.\n - For the server: the attacker can establish an HTTP/2 connection\n - For the client: the application makes a request to an attacker-controlled origin.\nHTTP/2 incoming headers exceeding the configured size limit are buffer in order to generate an informative HTTP 413 response. If a client does not stop sending headers, this leads to memory exhaustion.\n\n### Patches\n\nThe fix bounds the accumulated header-block size at `SETTINGS_MAX_HEADER_LIST_SIZE` (derived from `EmberServerBuilder.maxHeaderSize` / `EmberClientBuilder.maxResponseHeaderSize`). When a `CONTINUATION` frame would push the accumulated block over that limit, the connection is terminated with `GOAWAY`. The `receiveHeadersTimeout` additionally bounds how long an incomplete header block may remain open.\n\n### Workarounds\n\n- Disable HTTP/2 (`.withHttp2`) until upgraded (default). It is off by default.\n- If HTTP/2 must remain enabled, place ember behind a reverse proxy that terminates HTTP/2 and speaks HTTP/1.1 to ember.",
"id": "GHSA-cp4q-fqw9-4hf6",
"modified": "2026-09-15T20:01:08Z",
"published": "2026-09-15T20:01:08Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/http4s/http4s/security/advisories/GHSA-cp4q-fqw9-4hf6"
},
{
"type": "WEB",
"url": "https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e"
},
{
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
],
"summary": "Http4s Ember HTTP/2: unbounded continuation frame accumulation"
}
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