# CVE-2026-73495

## Summary

- **CVE ID:** CVE-2026-73495
- **Severity:** HIGH
- **CVSS Score:** 7.4 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N)
- **CWE:** CWE-444
- **Published:** Aug 12, 2026
- **Last Modified:** Aug 13, 2026

## 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.

## Affected Products

- http4s — blaze (< 0.23.18)
- http4s — blaze (>= 1.0.0-M1, < 1.0.0-M42)

## References

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

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.29%
- **EPSS Percentile:** 21.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._