{
  "affected": [
    {
      "database_specific": {
        "source": "https://cna.erlef.org/osv/EEF-CVE-2026-97200.json"
      },
      "package": {
        "ecosystem": "Hex",
        "name": "hackney",
        "purl": "pkg:hex/hackney"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0-beta.1"
            },
            {
              "fixed": "4.9.0"
            }
          ],
          "type": "SEMVER"
        }
      ],
      "versions": [
        "2.0.0",
        "2.0.0-beta.1",
        "2.0.1",
        "3.0.0",
        "3.0.1",
        "3.0.2",
        "3.0.3",
        "3.1.0",
        "3.1.1",
        "3.1.2",
        "3.2.0",
        "3.2.1",
        "4.0.0",
        "4.0.1",
        "4.0.2",
        "4.0.3",
        "4.1.0",
        "4.2.0",
        "4.2.1",
        "4.2.2",
        "4.2.3",
        "4.3.0",
        "4.4.0",
        "4.4.1",
        "4.4.2",
        "4.4.3",
        "4.4.5",
        "4.5.0",
        "4.5.1",
        "4.5.2",
        "4.6.0",
        "4.6.1",
        "4.7.0",
        "4.7.1",
        "4.7.2",
        "4.7.3",
        "4.7.4",
        "4.8.0",
        "4.8.1",
        "4.8.2",
        "4.8.3",
        "4.8.4",
        "4.8.5",
        "4.8.6",
        "4.8.7"
      ]
    },
    {
      "database_specific": {
        "source": "https://cna.erlef.org/osv/EEF-CVE-2026-97200.json"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "dc41b79339ca0c41e16d3f2dd17172bc2de855d6"
            },
            {
              "fixed": "493e8bf83a391548e5101792276ab3fc428fa76c"
            }
          ],
          "repo": "https://github.com/benoitc/hackney",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-97200"
  ],
  "credits": [
    {
      "name": "Martin Karrer",
      "type": "FINDER"
    },
    {
      "name": "Quinn Wilton",
      "type": "FINDER"
    },
    {
      "name": "Quinn Wilton",
      "type": "REPORTER"
    },
    {
      "name": "Martin Karrer",
      "type": "REMEDIATION_DEVELOPER"
    },
    {
      "name": "Benoit Chesneau",
      "type": "REMEDIATION_DEVELOPER"
    },
    {
      "name": "Jonatan Männchen / EEF",
      "type": "COORDINATOR"
    }
  ],
  "database_specific": {
    "capec_ids": [
      "CAPEC-130"
    ],
    "cpe_ids": [
      "cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:*"
    ],
    "cwe_ids": [
      "CWE-409",
      "CWE-770"
    ]
  },
  "details": "## Summary\n\nAllocation of Resources Without Limits or Throttling vulnerability in `hackney_conn` in benoitc hackney allows a malicious HTTP server to exhaust client memory via an oversized or highly compressed response body. `hackney:request/5` and `hackney:body/1` return the whole response body, and nothing bounds how much the connection process buffers. Any server the client requests can trigger it.\n\n`hackney_conn:read_full_body/2` and the HTTP/2 and HTTP/3 accumulators append every chunk until the body ends. With `{auto_decompress, true}` the buffered body is then inflated in one step with `zlib:gunzip/1` or `zlib:inflate/2`, which return the whole output at once.\n\nThis issue affects hackney: from 2.0.0-beta.1 before 4.9.0.\n\n## Details\n\n**1. Unbounded accumulation.** `hackney:request/5` with a body, and `hackney:body/1` after `start_response/1`, read the response in `src/hackney_conn.erl` through `read_full_body/2`, which appends each chunk to a binary accumulator until the body ends. The HTTP/2 and HTTP/3 synchronous paths accumulate stream data the same way. No option caps the size.\n\n**2. One-step decompression.** With `{auto_decompress, true}` hackney sends `Accept-Encoding: gzip, deflate`. Once the body is complete, `maybe_decompress_body/2` dispatches on `Content-Encoding` to `decompress_gzip/1` (`zlib:gunzip/1`) or `decompress_deflate/1` (`zlib:inflate/2`). Both return the whole output at once, so the inflated size is bounded only by the compression ratio. The report measured a 1 MB gzip body inflating to 1 GB on hackney 4.8.4.\n\n## Proof of concept\n\n1. Build a gzip stream whose inflated size is 1 GB from a reused 64 KB chunk of zero bytes (deflate with window bits 31, best compression). The stream is about 1 MB on the wire.\n2. Start a TCP listener on loopback that accepts one connection, reads the request, and answers `HTTP/1.1 200 OK` with `Content-Encoding: gzip`, a `Content-Length` matching the stream, `Connection: close`, and the stream as body.\n3. From a node running a vulnerable hackney, call `hackney:request(get, Url, [], <<>>, [{auto_decompress, true}, with_body])` against that listener.\n4. Observe the returned body of 1,048,576,000 bytes and the VM memory growing by about 1.8 GB for a 1,019,197 byte response. A larger stream, or an endless body without `auto_decompress`, drives the node out of memory.\n\n## Impact\n\nA server the client requests can make the client allocate memory proportional to the body it sends, or to its decompressed size, until the node runs out of memory.\n\n## Workarounds\n\nLeave `auto_decompress` disabled (the default). Without it `hackney_conn:maybe_decompress_body/2` never inflates the body, which closes the amplification half. The uncapped raw body read has no workaround.",
  "id": "EEF-CVE-2026-97200",
  "modified": "2026-10-26T14:00:04.842482189Z",
  "published": "2026-10-26T13:49:40.392Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/benoitc/hackney/releases/tag/4.9.0"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-97200.html"
    },
    {
      "type": "WEB",
      "url": "https://github.com/benoitc/hackney/pull/980"
    },
    {
      "type": "WEB",
      "url": "https://github.com/benoitc/hackney/commit/dc41b79339ca0c41e16d3f2dd17172bc2de855d6"
    },
    {
      "type": "FIX",
      "url": "https://github.com/benoitc/hackney/commit/493e8bf83a391548e5101792276ab3fc428fa76c"
    },
    {
      "type": "PACKAGE",
      "url": "https://hex.pm/packages/hackney"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Unbounded response body buffering and decompression in hackney"
}