CVE-2026-73495

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.

CVSS 3.1

7.4CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

0.5% chance of exploitation in the next 30 days; higher than 41% of CVEs (scores of 2026-10-25)

CWE

CWE-444

Published

2026-08-12

Modified

2026-10-24

Record from

the NVD, synced 2026-10-24

Packages (OSV)

References

• https://github.com/http4s/blaze/commit/ef3e666c146cfc16cb6603f1fc3c464daab4a24f
• https://github.com/http4s/blaze/releases/tag/v0.23.18
• https://github.com/http4s/blaze/releases/tag/v1.0.0-M42
• https://github.com/http4s/blaze/security/advisories/GHSA-46q4-43ph-c6fr

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