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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http4s组织开源的一个Scala的HTTP服务框架。 http4s 0.23.35之前版本和1.0.0-M1至1.0.0-M47之前版本存在资源管理错误漏洞，该漏洞源于Ember服务器启用HTTP/2时未对等端创建的流强制执行SETTINGS_MAX_CONCURRENT_STREAMS限制，且未强制执行enablePush，未经身份验证的攻击者可通过单个连接打开无限数量的流或利用服务器发起的PUSH_PROMISE帧，导致堆内存耗尽。

CVSS 7.5 · High EPSS 0.63% · P50

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
Vulnerability Title
http4s 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
http4s是http4s组织开源的一个Scala的HTTP服务框架。 http4s 0.23.35之前版本和1.0.0-M1至1.0.0-M47之前版本存在资源管理错误漏洞，该漏洞源于Ember服务器启用HTTP/2时未对等端创建的流强制执行SETTINGS_MAX_CONCURRENT_STREAMS限制，且未强制执行enablePush，未经身份验证的攻击者可通过单个连接打开无限数量的流或利用服务器发起的PUSH_PROMISE帧，导致堆内存耗尽。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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