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CVE-2026-54556— Http4s: HTTP/2 Denial of Service with Ember Backend

Quick assessment

Affected
http4s http4s
Exploitation
Public or AI PoC available; prioritize validation
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-M47之前版本存在资源管理错误漏洞，该漏洞源于HPACK封装器在启用HTTP/2的Ember后端拼接HEADERS和CONTINUATION帧片段时，maxHeaderSize计算未包含索引标头或HPACK每标头开销，导致小型压缩标头块扩展为更大解码表示，可能允许未经身份验证的HTTP/2对等方通过并发恶意连接耗尽进程堆，导致拒绝服务。

CVSS 8.2 · High EPSS 0.52% · P43

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 7

VendorProduct Version RangeStatus
http4s http4s < 0.23.35 affected
>= 1.0.0-M1, < 1.0.0-M46 affected
org.http4s http4s-ember-core_2.12 < 0.23.35 affected
org.http4s http4s-ember-core_2.13 >= 1.0.0-M1, < 1.0.0-M46 affected
< 0.23.35 affected
org.http4s http4s-ember-core_3 >= 1.0.0-M1, < 1.0.0-M46 affected
< 0.23.35 affected
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I. Basic Information for CVE-2026-54556

Vulnerability Information
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Vulnerability Title
Http4s: HTTP/2 Denial of Service with Ember Backend
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 unauthenticated HTTP/2 peer can cause an out-of-memory denial of service in the Ember backend with HTTP/2 enabled. The Hpack wrapper in ember-core/shared/src/main/scala/org/http4s/ember/core/h2/Hpack.scala concatenates HEADERS and CONTINUATION frame fragments and decodes them into a single List, but maxHeaderSize accounting does not include indexed headers or HPACK per-header overhead. A small compressed header block can therefore expand into a much larger decoded representation that remains in memory for processing. Servers exposed to untrusted HTTP/2 traffic and clients directed to an untrusted HTTP/2 server are affected, and concurrent malicious connections can exhaust the process heap. This issue is fixed in versions 0.23.35 and 1.0.0-M47.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
对高度压缩数据的处理不恰当(数据放大攻击)
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-M47之前版本存在资源管理错误漏洞，该漏洞源于HPACK封装器在启用HTTP/2的Ember后端拼接HEADERS和CONTINUATION帧片段时，maxHeaderSize计算未包含索引标头或HPACK每标头开销，导致小型压缩标头块扩展为更大解码表示，可能允许未经身份验证的HTTP/2对等方通过并发恶意连接耗尽进程堆，导致拒绝服务。
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 < 0.23.35 -
org.http4s http4s-ember-core_2.12 < 0.23.35 -
org.http4s http4s-ember-core_2.13 >= 1.0.0-M1, < 1.0.0-M46 -
org.http4s http4s-ember-core_3 >= 1.0.0-M1, < 1.0.0-M46 -

II. Public POCs for CVE-2026-54556

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8891 chars
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III. Intelligence Information for CVE-2026-54556

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Vendor Advisories for CVE-2026-54556 (1)

Vendor Pages for CVE-2026-54556 (2)

IV. Related Vulnerabilities

Same product: http4s
Same vendor: http4s
Same weakness: CWE-409

V. Comments for CVE-2026-54556

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