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CVE-2026-69213— Http4s Ember HTTP/2: unbounded outbound frame queue

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 Scala 语言中用于 HTTP 服务的接口库。在 0.23.35 和 1.0.0-M47 之前的版本中，Ember 实现（Http4s 的默认服务器实现）在处理 HTTP/2 出站帧时，通过一个无界队列（unbounded queue）进行序列化，该队列由 writeLoop 消费。 当对端（peer）停止读取数据时，一个未经身份验证的 HTTP/2 客户端可以持续发送 PING、SETTINGS 或 DATA 帧，导致 Ember 以快于 writer 消费的速度向队列中追加确认帧（ACK）或

CVSS 7.5 · High

Possible ATT&CK Techniques 1 AI

T1298

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-2026-69213

Vulnerability Information
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Vulnerability Title
Http4s Ember HTTP/2: unbounded outbound frame queue
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, Ember HTTP/2 serializes outbound frames through one unbounded queue consumed by writeLoop. When the peer stops reading, an unauthenticated HTTP/2 client can continue sending PING, SETTINGS, or DATA frames that cause Ember to enqueue acknowledgments or WINDOW_UPDATE frames faster than the writer drains them, exhausting heap memory on a server built with withHttp2. The shared behavior also affects an ember-client connected to a hostile HTTP/2 server, and the patch replaces the unbounded path with bounded, backpressured outbound queues. 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-2026-69213

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III. Intelligence Information for CVE-2026-69213

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Patches & Fixes for CVE-2026-69213 (1)

Vendor Advisories for CVE-2026-69213 (1)

Vendor Pages for CVE-2026-69213 (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-2026-69208 7.5 HIGH Http4s: DigestAuth nonce map grows unbounded
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-2026-69203 7.5 HIGH Http4s Ember HTTP/2: does not enforce SETTINGS_MAX_CONCURRENT_STREAMS
CVE-2026-69209 7.5 HIGH Http4s: WebSocket decoder accepts unbounded message sizes
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-2026-69213

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