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CVE-2026-88975— Http4s: Ember HTTP/2 buffers a frame's declared payload before checking SETTINGS_MAX_FRAME_SIZE

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 0.23.37之前版本和1.0.0-M1至1.0.0-M48之前版本存在资源管理错误漏洞，该漏洞源于Ember的HTTP/2读取循环解析帧的24位声明长度后，在将整个有效载荷与SETTINGS_MAX_FRAME_SIZE比较前就进行缓冲，未经身份验证的对端可声明接近16 MiB的有效载荷，而Ember通告为16 KiB，导致每个连接最多1024倍内存放大，可能造成拒绝服务。

CVSS 7.5 · High EPSS 0.63% · P50

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 2

VendorProduct Version RangeStatus
http4s http4s < 0.23.37 affected
>= 1.0.0-M1, < 1.0.0-M48 affected
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I. Basic Information for CVE-2026-88975

Vulnerability Information
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Vulnerability Title
Http4s: Ember HTTP/2 buffers a frame's declared payload before checking SETTINGS_MAX_FRAME_SIZE
Source: CVE Program / CVE List V5
Vulnerability Description
Http4s is a Scala interface for HTTP services. Prior to 0.23.37 and 1.0.0-M48, Ember’s HTTP/2 read loop parses a frame’s 24-bit declared length but waits to buffer the entire payload before comparing it with SETTINGS_MAX_FRAME_SIZE. An unauthenticated peer can declare a payload near 16 MiB on a connection where Ember advertised 16 KiB and either complete or slowly stream it, causing up to 1024-fold memory amplification per connection before processFrame can reject the frame. The shared H2Connection.readLoop affects withHttp2 servers and clients, while HTTP/2-disabled configurations are unaffected, and the patch rejects oversized frames before buffering their payloads. This issue is fixed in versions 0.23.37 and 1.0.0-M48.
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 0.23.37之前版本和1.0.0-M1至1.0.0-M48之前版本存在资源管理错误漏洞，该漏洞源于Ember的HTTP/2读取循环解析帧的24位声明长度后，在将整个有效载荷与SETTINGS_MAX_FRAME_SIZE比较前就进行缓冲，未经身份验证的对端可声明接近16 MiB的有效载荷，而Ember通告为16 KiB，导致每个连接最多1024倍内存放大，可能造成拒绝服务。
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 < 0.23.37 -

II. Public POCs for CVE-2026-88975

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III. Intelligence Information for CVE-2026-88975

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Patches & Fixes for CVE-2026-88975 (1)

Vendor Advisories for CVE-2026-88975 (2)

Vendor Pages for CVE-2026-88975 (1)

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-2026-69202 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-2026-69203 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