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CVE-2026-69203— Http4s Ember HTTP/2: does not enforce SETTINGS_MAX_CONCURRENT_STREAMS

Quick assessment

Affected
http4s http4s
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Http4s 是用于 HTTP 服务的 Scala 接口。在版本 0.23.35 和 1.0.0-M47 之前，通过 启用 HTTP/2 的 Ember 服务器并未对对端创建的流强制执行 限制。单个未认证连接可以打开无限数量的流，每个流都会保留其状态直至导致堆内存耗尽。此外，由于 未被强制检查，相同的无限制分配问题也可通过 Ember 客户端利用服务器发起的 帧触发。该问题已在版本 0.23.35 和 1.0.0-M47 中修复。

CVSS 7.5 · High

Possible ATT&CK Techniques 1 AI

T1210 · Exploitation of Remote Services

Affected Version Matrix 2

VendorProduct Version RangeStatus
http4s http4s < 0.23.35 affected
>= 1.0.0-M1, < 1.0.0-M47 affected
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I. Basic Information for CVE-2026-69203

Vulnerability Information
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Vulnerability Title
Http4s Ember HTTP/2: does not enforce SETTINGS_MAX_CONCURRENT_STREAMS
Source: CVE Program / CVE List V5
Vulnerability Description
Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, An Ember server with HTTP/2 enabled through withHttp2 does not enforce SETTINGS_MAX_CONCURRENT_STREAMS for peer-created streams. One unauthenticated connection can open an unbounded number of streams, each retaining per-stream state until heap exhaustion. The same unchecked allocation is reachable in an ember-client through server-initiated PUSH_PROMISE frames because enablePush is not enforced. This issue is fixed in versions 0.23.35 and 1.0.0-M47.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
http4s http4s < 0.23.35 -

II. Public POCs for CVE-2026-69203

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III. Intelligence Information for CVE-2026-69203

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Patches & Fixes for CVE-2026-69203 (1)

Vendor Advisories for CVE-2026-69203 (1)

Vendor Pages for CVE-2026-69203 (2)

Same Patch Batch · http4s · 2026-09-15 · 18 CVEs total

CVE-2026-69204 9.2 CRITICAL Http4s: Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggl
CVE-2026-69217 8.7 HIGH Http4s: Ember Server accepts duplicate Content-Length headers
CVE-2026-69205 8.7 HIGH Http4s: Ember Transfer-Encoding value parsing (TE.CL / TE.0 request smuggling)
CVE-2026-88975 7.5 HIGH Http4s: Ember HTTP/2 buffers a frame's declared payload before checking SETTINGS_MAX_FRAME
CVE-2026-69202 7.5 HIGH Http4s Ember HTTP/2: unbounded inbound body buffering
CVE-2026-69218 7.5 HIGH Http4s Ember HTTP/2: unbounded continuation frame accumulation
CVE-2026-69210 7.5 HIGH Http4s: WebSocket decoder accepts negative length, causing infinite decode loop
CVE-2026-69213 7.5 HIGH Http4s Ember HTTP/2: unbounded outbound frame queue
CVE-2026-69209 7.5 HIGH Http4s: WebSocket decoder accepts unbounded message sizes
CVE-2026-69208 7.5 HIGH Http4s: DigestAuth nonce map grows unbounded
CVE-2026-69214 6.8 MEDIUM Http4s: CookieJar middleware accepts arbitrary Set-Cookie domain
CVE-2026-69215 6.8 MEDIUM Http4s: CookieJar middleware matches by substring, leaking cookies cross-origin
CVE-2026-69201 5.9 MEDIUM Http4s: ResourceService and Webjar Service path escape via percent-encoded separators
CVE-2026-69212 5.9 MEDIUM Http4s: FollowRedirect middleware leaks credentials over https->http same-authority redire
CVE-2026-69206 5.9 MEDIUM Http4s: DigestAuth allows replay of captured requests
CVE-2026-69216 5.4 MEDIUM Http4s: Ember chunk parser lenience (TE.TE request smuggling)
CVE-2026-69211 4.8 MEDIUM Http4s: Set-Cookie rendering does not escape attribute delimiters

IV. Related Vulnerabilities

Same product: http4s
Same vendor: http4s
Same weakness: CWE-400

V. Comments for CVE-2026-69203

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