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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-73495
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-12 22:17:16 UTC
Updated2026-08-12 22:17:16 UTC
Descriptionblaze 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.

Risk And Classification

Primary CVSS: v3.1 7.4 HIGH from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Problem Types: CWE-444 | CWE-444 CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.4HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
3.1CNADECLARED7.4HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Http4s Blaze affected < 0.23.18 Not specified
CNA Http4s Blaze affected >= 1.0.0-M1, < 1.0.0-M42 Not specified

References

ReferenceSourceLinkTags
github.com/http4s/blaze/releases/tag/v1.0.0-M42 [email protected] github.com
github.com/http4s/blaze/security/advisories/GHSA-46q4-43ph-c6fr [email protected] github.com
github.com/http4s/blaze/releases/tag/v0.23.18 [email protected] github.com
github.com/http4s/blaze/commit/ef3e666c146cfc16cb6603f1fc3c464daab4a24f [email protected] github.com
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