GHSA-m4w9-hjfw-vwj4: http4k `HmacSha256.hash` (despite The `Hmac` Naming) Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-m4w9-hjfw-vwj4",
  "modified" : "2026-06-19T21:16:03Z",
  "published" : "2026-06-19T21:16:03Z",
  "aliases" : [ ],
  "summary" : "http4k: `HmacSha256.hash` (despite the `Hmac` naming) computed a plain unkeyed digest; clarified by deprecation in favour of `Sha256.hash` / `Sha256.hmac`",
  "details" : "### Impact\n\nThe `HmacSha256` class contained two functions:\n- `hash(payload)` — a plain unkeyed SHA-256 digest. The `Hmac` prefix in the class name was misleading; this function has no key parameter, so it could never have been an HMAC.\n- `hmacSHA256(key, data)` — a properly keyed HMAC-SHA256.\n\nA reader who didn't engage with the function signature could in principle have assumed `HmacSha256.hash(payload)` was somehow keyed, but the absence of any key parameter made that misuse unlikely in practice.\n\n**Who is affected:** any downstream caller who read the class name and used `HmacSha256.hash` as a message authentication code without noticing it takes no key. **Verified at v6.47.2.0: zero internal misuse in http4k itself.** Both production usages of `HmacSha256.hash` (AWS SigV4 canonical-request hashing in `AwsSignatureV4Signer.kt` and `x-amz-content-sha256` in `awsExtensions.kt`) are AWS-spec-correct uses of plain SHA-256; every keyed `hmacSHA256(key, data)` call passes a real key. The advisory exists so any downstream caller relying on the misleadingly-named API knows to migrate.\n\n### Patches\n\nUpgrade to **6.49.0.0** or later. The fix introduces:\n- `Sha256.hash(input)` — unkeyed digest (the actual behaviour `HmacSha256.hash` provided).\n- `Sha256.hmac(key, input)` — keyed HMAC-SHA256 (the behaviour the name implied).\n\n`HmacSha256` is deprecated. Existing callers continue to work via deprecation shims; migrate to `Sha256.hash` or `Sha256.hmac` per intent.\n\n### Workarounds\n\nIf you cannot upgrade and you need a real HMAC-SHA256, use `javax.crypto.Mac.getInstance(\"HmacSHA256\")` with a `SecretKeySpec`. For an unkeyed SHA-256 digest, use `java.security.MessageDigest.getInstance(\"SHA-256\")`. The keyed `hmacSHA256(key, data)` was always correctly implemented and is safe to use as-is.\n\n### References\n\n- Fix release: [v6.49.0.0](https://github.com/http4k/http4k/releases/tag/6.49.0.0)\n- Background: [RFC 2104 — HMAC: Keyed-Hashing for Message Authentication](https://datatracker.ietf.org/doc/html/rfc2104)",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4k:http4k-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.49.0.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/http4k/http4k/security/advisories/GHSA-m4w9-hjfw-vwj4"
  }, {
    "type" : "WEB",
    "url" : "https://datatracker.ietf.org/doc/html/rfc2104"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/http4k/http4k"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/http4k/http4k/releases/tag/6.49.0.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-345" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-19T21:16:03Z",
    "nvd_published_at" : null
  }
}