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CVE-2026-73495— blaze: Chunked-body trailer fields promoted into Request.headers in blaze-server (front-end header-sanitization bypass)

Quick assessment

Affected
http4s blaze
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 blaze是http4s组织的一款Web中间件组件。 http4s blaze 0.23.18之前版本和1.0.0-M42之前版本存在输入验证错误漏洞，该漏洞源于blaze-server将HTTP/1.1分块传输的trailer字段合并到Request.headers中，未经身份验证的远程攻击者可注入任意标头和值，绕过基于标头的信任决策，可能导致伪造客户端IP、伪造https协议、注入内部授权头或终止后端连接。

CVSS 7.4 · High EPSS 0.48% · P40

Affected Version Matrix 2

VendorProduct Version RangeStatus
http4s blaze < 0.23.18 affected
>= 1.0.0-M1, < 1.0.0-M42 affected
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I. Basic Information for CVE-2026-73495

Vulnerability Information
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Vulnerability Title
blaze: Chunked-body trailer fields promoted into Request.headers in blaze-server (front-end header-sanitization bypass)
Source: CVE Program / CVE List V5
Vulnerability Description
blaze is a Scala library for building asynchronous pipelines, with a focus on network IO. Prior to 0.23.18 and 1.0.0-M42, blaze-server can merge HTTP/1.1 chunked-body trailer fields into Request.headers. Because trailer fields are attacker-controlled, an unauthenticated remote client can inject arbitrary header names and values, including X-Forwarded-For and internal authorization headers, that a fronting proxy sanitized from the request-header section, bypassing header-based trust decisions in the application. Any http4s application using BlazeServerBuilder over HTTP/1.1 whose routes or middleware trust proxy-set headers, including X-Forwarded-For, X-Real-IP, and X-Forwarded-Host, is affected. If a fronting proxy strips or normalizes those headers but forwards chunked bodies with trailers intact, an attacker can spoof client IP for allow-lists, rate limits, or auditing, forge the https scheme, or inject internal authorization headers. A promoted Connection: close trailer is also honored, allowing attacker-controlled termination of pooled backend connections. This issue is fixed in versions 0.23.18 and 1.0.0-M42.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
HTTP请求的解释不一致性(HTTP请求私运)
Source: CVE Program / CVE List V5
Vulnerability Title
http4s blaze 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
http4s blaze是http4s组织的一款Web中间件组件。 http4s blaze 0.23.18之前版本和1.0.0-M42之前版本存在输入验证错误漏洞，该漏洞源于blaze-server将HTTP/1.1分块传输的trailer字段合并到Request.headers中，未经身份验证的远程攻击者可注入任意标头和值，绕过基于标头的信任决策，可能导致伪造客户端IP、伪造https协议、注入内部授权头或终止后端连接。
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 blaze < 0.23.18 -

II. Public POCs for CVE-2026-73495

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 9657 chars
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III. Intelligence Information for CVE-2026-73495

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Patches & Fixes for CVE-2026-73495 (1)

Vendor Advisories for CVE-2026-73495 (1)

Vendor Pages for CVE-2026-73495 (2)

IV. Related Vulnerabilities

Same product: blaze
Same vendor: http4s
Same weakness: CWE-444

V. Comments for CVE-2026-73495

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