{"id":"CVE-2026-73495","aliases":["GHSA-46q4-43ph-c6fr"],"url":"https://o3.security/vulnerability/CVE-2026-73495","summary":"blaze: Chunked-body trailer fields promoted into Request.headers in blaze-server (front-end header-sanitization bypass)","details":"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.","published":"2026-08-12T21:11:55.180Z","modified":"2026-09-11T03:30:17.722081879Z","cvss":{"score":7.4,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"},"epss":{"score":0.00289,"percentile":0.21569,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Maven","name":"org.http4s:blaze-http_2.13","fixedVersion":"0.23.18"},{"ecosystem":"Maven","name":"org.http4s:blaze-http_2.12","fixedVersion":"0.23.18"},{"ecosystem":"Maven","name":"org.http4s:blaze-http_3","fixedVersion":"0.23.18"},{"ecosystem":"Maven","name":"org.http4s:blaze-http_3","fixedVersion":"1.0.0-M42"},{"ecosystem":"Maven","name":"org.http4s:blaze-http_2.13","fixedVersion":"1.0.0-M42"}],"fix":{"url":"https://github.com/http4s/blaze/commit/ef3e666c146cfc16cb6603f1fc3c464daab4a24f","label":"http4s/blaze@ef3e666"},"references":[{"type":"WEB","url":"https://github.com/http4s/blaze/releases/tag/v0.23.18"},{"type":"WEB","url":"https://github.com/http4s/blaze/releases/tag/v1.0.0-M42"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73495.json"},{"type":"ADVISORY","url":"https://github.com/http4s/blaze/security/advisories/GHSA-46q4-43ph-c6fr"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-73495"},{"type":"FIX","url":"https://github.com/http4s/blaze/commit/ef3e666c146cfc16cb6603f1fc3c464daab4a24f"},{"type":"PACKAGE","url":"https://github.com/http4s/blaze"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-11T03:30:17.722081879Z"}}