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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 是一个用于 HTTP 服务的 Scala 接口。在 0.23.35 和 1.0.0-M47 之前的版本中，启用 HTTP/2 的 Ember 后端存在一个内存溢出型拒绝服务（OOM DoS）漏洞，未认证的 HTTP/2 对等方可触发该漏洞。位于 中的 Hpack 封装器会将 HEADERS 和 CONTINUATION 帧片段进行拼接并解码为一个 List，但其 的统计未包含索引头或 HPACK 的每头开销。因此，一个小型的压缩头块在解码后可能扩展为占用大量内存的表示形式，并保留在内存中以待处理。暴露

CVSS 8.2 · High

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

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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