{"id":"GHSA-46q4-43ph-c6fr","title":"blaze: Chunked-body trailer fields promoted into Request.headers in blaze-server (front-end header-sanitization bypass)","summary":"blaze: Chunked-body trailer fields promoted into Request.headers in blaze-server (front-end header-sanitization bypass)","severity":"high","cvss":7.4,"cwe":["CWE-444"],"vendor":"http4s","product":"org.http4s:blaze-http_2.13","ecosystem":"maven","affected":["org.http4s:blaze-http_2.13 <= 0.23.17","org.http4s:blaze-http_2.12 <= 0.23.17","org.http4s:blaze-http_3 <= 0.23.17","org.http4s:blaze-http_3 >= 1.0.0-M1, < 1.0.0-M42","org.http4s:blaze-http_2.13 >= 1.0.0-M1, <= 1.0.0-M41"],"patched":["org.http4s:blaze-http_2.13 0.23.18","org.http4s:blaze-http_2.12 0.23.18","org.http4s:blaze-http_3 0.23.18","org.http4s:blaze-http_3 1.0.0-M42","org.http4s:blaze-http_2.13 1.0.0-M42"],"published":"2026-07-24","updated":"2026-07-24","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-46q4-43ph-c6fr","references":[{"url":"https://github.com/http4s/blaze/security/advisories/GHSA-46q4-43ph-c6fr"},{"url":"https://github.com/http4s/blaze/commit/ef3e666c146cfc16cb6603f1fc3c464daab4a24f"},{"url":"https://github.com/http4s/blaze/releases/tag/v0.23.18"},{"url":"https://github.com/http4s/blaze/releases/tag/v1.0.0-M42"},{"url":"https://github.com/advisories/GHSA-46q4-43ph-c6fr"}],"tags":["ghsa","maven"],"ingestedAt":"2026-07-24T22:40:26.707Z","slug":"GHSA-46q4-43ph-c6fr","body":"## Overview\n\n### Summary\n  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/values (e.g. `X-Forwarded-For`, internal-auth headers) that a fronting proxy sanitized from the request-header section, bypassing header-based trust decisions in the application.\n\n  ### Impact\n  Any http4s application using `BlazeServerBuilder` over HTTP/1.1 whose routes or middleware trust proxy-set headers (e.g., `X-Forwarded-For`, `X-Real-IP`, `X-Forwarded-Host`, org-internal auth headers) is affected. Where a fronting proxy strips/normalizes those headers but forwards chunked bodies with trailers intact, an attacker can spoof client IP for allow-lists/rate-limits/audit, forge the `https` scheme, or inject internal-auth headers. A promoted `Connection: close` trailer is also honored, allowing attacker-controlled termination of pooled backend connections.\n\n  ### Workarounds\n  Deploy behind a proxy that removes trailer fields (or rejects requests that use trailers) before forwarding; until patched, avoid trust decisions based on headers that a proxy is relied upon to sanitize.\n\n## Affected packages\n\n- `org.http4s:blaze-http_2.13 <= 0.23.17`\n- `org.http4s:blaze-http_2.12 <= 0.23.17`\n- `org.http4s:blaze-http_3 <= 0.23.17`\n- `org.http4s:blaze-http_3 >= 1.0.0-M1, < 1.0.0-M42`\n- `org.http4s:blaze-http_2.13 >= 1.0.0-M1, <= 1.0.0-M41`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `org.http4s:blaze-http_2.13 0.23.18`\n- `org.http4s:blaze-http_2.12 0.23.18`\n- `org.http4s:blaze-http_3 0.23.18`\n- `org.http4s:blaze-http_3 1.0.0-M42`\n- `org.http4s:blaze-http_2.13 1.0.0-M42`","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":40.7,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}