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

Type: advisorySources: OSV

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.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-73495
Confirmed fixed CVEs
Not specified
Updated in this feed
3 Nov 2026, 19:32 UTC · Revision 1

Source evidence

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

core-osv · Original source

Published 12 Aug 2026, 21:11 UTC

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.

osv:CVE-2026-73495
Complete source record
{
  "id": "82532e04357d8eefa7b1991b5b9d21be91a8c8a80753d402749c53bcf9e1f4aa",
  "url": "https://osv.dev/vulnerability/CVE-2026-73495",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "blaze: Chunked-body trailer fields promoted into Request.headers in blaze-server (front-end header-sanitization bypass)",
    "summary": "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.",
    "evidence": "osv:CVE-2026-73495",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-73495",
      "aliases": [
        "CVE-2026-73495",
        "GHSA-46q4-43ph-c6fr"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/http4s/blaze",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "2ae13a74d55209b6573d5228d1aa94f0361a75d0"
                },
                {
                  "fixed": "b2cb8e8591391409bb1df242b45433891251b1b1"
                },
                {
                  "fixed": "ef3e666c146cfc16cb6603f1fc3c464daab4a24f"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "0.23.18"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "introduced": "1.0.0-M1"
                      },
                      {
                        "fixed": "1.0.0-M42"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "ef3e666c146cfc16cb6603f1fc3c464daab4a24f"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "2ae13a74d55209b6573d5228d1aa94f0361a75d0"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v0.23.18"
                  },
                  {
                    "range": [
                      {
                        "fixed": "b2cb8e8591391409bb1df242b45433891251b1b1"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v1.0.0-M42"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v1.0.0-M41",
            "v0.23.17",
            "v1.0.0-M40",
            "v0.23.16",
            "v1.0.0-M39",
            "v0.23.15",
            "v0.23.14",
            "v1.0.0-M38",
            "v1.0.0-M37",
            "v0.23.13",
            "v1.0.0-M36",
            "v1.0.0-M35",
            "v1.0.0-M34",
            "v1.0.0-M33",
            "v0.23.12",
            "v0.15.3",
            "v0.15.2",
            "v0.15.1",
            "v0.15.0",
            "v0.15.0-M4",
            "v0.15.0-M3",
            "v0.15.0-M2",
            "v0.15.0-M1",
            "v0.14.14",
            "v0.14.13",
            "v0.14.12",
            "v0.14.10",
            "v0.14.8",
            "v0.14.7",
            "v0.14.6",
            "v0.14.5",
            "v0.14.4",
            "v0.14.2",
            "v0.14.0",
            "v0.14.0-M12",
            "v0.14.0-M11",
            "v0.14.0-M10",
            "v0.14.0-M9",
            "v0.14.0-M7",
            "v0.14.0-M3",
            "v0.14.0-M2",
            "v0.13.0",
            "v0.12.0",
            "v0.11.0",
            "v0.10.0",
            "v0.9.0",
            "v0.8.1",
            "v0.8.0",
            "v0.7.0",
            "v0.6.0",
            "v0.5.0",
            "v0.4.0",
            "v0.3.0",
            "v0.2.0",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-73495.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:31.686448798Z",
      "provider": "osv",
      "references": [
        "https://github.com/http4s/blaze/releases/tag/v0.23.18",
        "https://github.com/http4s/blaze/releases/tag/v1.0.0-M42",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73495.json",
        "https://github.com/http4s/blaze/security/advisories/GHSA-46q4-43ph-c6fr",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-73495",
        "https://github.com/http4s/blaze/commit/ef3e666c146cfc16cb6603f1fc3c464daab4a24f"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-444"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/73xxx/CVE-2026-73495.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-73495",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 498737,
  "published_at": "2026-08-12T21:11:55.18+00:00"
}