CVE-2026-53659: http4k Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-g4w2-6h2r-3m3w",
  "modified" : "2026-08-17T21:58:23Z",
  "published" : "2026-08-17T21:52:27Z",
  "aliases" : [ "CVE-2026-53659" ],
  "summary" : "http4k: Unbounded gzip decompression in `ServerFilters.GZip` / `RequestFilters.GunZip` allowed memory-exhaustion DoS",
  "details" : "### Impact\n\n`ServerFilters.GZip` and `RequestFilters.GunZip` (and the underlying `Gzip` functions used to decompress request bodies) did not impose any cap on the decompressed size. A small malicious gzip-encoded request body (on the order of kilobytes) could decompress to gigabytes, exhausting the JVM heap and denying service to other clients.\n\n**Who is affected:** any http4k server that accepts gzip-encoded requests via `ServerFilters.GZip` or `RequestFilters.GunZip`. Exploitable by any unauthenticated client. The vulnerability was introduced on 2017-08-01 (commit `2618fe08f9`) and was present for ~9 years.\n\n### Patches\n\n| Line | Fixed in | Edition |\n|------|----------|---------|\n| v6.x (Community) | **6.49.0.0** | Community |\n| v5.x (LTS) | **5.42.0.0** | Enterprise — contact [enterprise@http4k.org](mailto:enterprise@http4k.org) |\n| v4.x (LTS) | **4.51.0.0** | Enterprise — contact [enterprise@http4k.org](mailto:enterprise@http4k.org) |\n\nThe fix caps decompression at 10MB by default; oversized requests through `ServerFilters.GZip` / `RequestFilters.GunZip` now return `413 Request Entity Too Large`, and decompressing elsewhere throws `SizeLimitExceededException`. The keyed `hmacSHA256` helper and other safe paths are unaffected.\n\n### Workarounds\n\nFor deployments that cannot upgrade immediately:\n- Replace the `GZip` / `GunZip` filters with custom versions that wrap the decompressed `InputStream` in a size-limited reader, or\n- Strip gzip-encoded request support at the edge (CDN, reverse proxy, or load balancer).\n\n### References\n\n- Vulnerability introduced: [`2618fe08f9`](https://github.com/http4k/http4k/commit/2618fe08f9)\n- Fix release: [v6.49.0.0](https://github.com/http4k/http4k/releases/tag/6.49.0.0)\n- Background: [CWE-409 — Improper Handling of Highly Compressed Data](https://cwe.mitre.org/data/definitions/409.html)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4k:http4k-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "6.0.0.0"
      }, {
        "fixed" : "6.49.0.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4k:http4k-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "5.0.0.0"
      }, {
        "fixed" : "5.42.0.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.http4k:http4k-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "4.48.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/http4k/http4k/security/advisories/GHSA-g4w2-6h2r-3m3w"
  }, {
    "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-409" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-17T21:52:27Z",
    "nvd_published_at" : null
  }
}