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Decompression bomb DoS in Req via auto-decoded archive and compressed response bodies

Type: advisorySources: OSV

Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in wojtekmach Req allows attacker-controlled HTTP servers to exhaust memory in a Req client via decompression-bomb response bodies. Req's default response pipeline includes Req.Steps.decode_body/1 and Req.Steps.decompress_body/1 in lib/req/steps.ex. decode_body/1 dispatches on the server-supplied content-type (or URL extension) and calls :zip.extract(body, [:memory]) for application/zip, :erl_tar.extract({:binary, body}, [:memory]) for application/x-tar, and :erl_tar.extract({:binary, body}, [:memory, :compressed]) for application/gzip / .tgz. Each returns the full decompressed archive contents as a [{name, bytes}] list in memory, with no per-entry or total size cap. decompress_body/1 walks the content-encoding header and chains :zlib/:brotli/:ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip inflates through multiple layers without bound. Both steps are enabled by default, no caller opt-in is required, and the attacker controls the content-type and content-encoding headers on their own server (or on any host reached via Req's automatic redirect following). A sub-megabyte response can expand to multiple gigabytes on the victim, crashing the BEAM process. This issue affects req: from 0.1.0 before 0.6.1.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-49755
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 05:19 UTC · Revision 1

Source evidence

Decompression bomb DoS in Req via auto-decoded archive and compressed response bodies

core-osv · Original source

Published 8 Jun 2026, 15:20 UTC

Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in wojtekmach Req allows attacker-controlled HTTP servers to exhaust memory in a Req client via decompression-bomb response bodies. Req's default response pipeline includes Req.Steps.decode_body/1 and Req.Steps.decompress_body/1 in lib/req/steps.ex. decode_body/1 dispatches on the server-supplied content-type (or URL extension) and calls :zip.extract(body, [:memory]) for application/zip, :erl_tar.extract({:binary, body}, [:memory]) for application/x-tar, and :erl_tar.extract({:binary, body}, [:memory, :compressed]) for application/gzip / .tgz. Each returns the full decompressed archive contents as a [{name, bytes}] list in memory, with no per-entry or total size cap. decompress_body/1 walks the content-encoding header and chains :zlib/:brotli/:ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip inflates through multiple layers without bound. Both steps are enabled by default, no caller opt-in is required, and the attacker controls the content-type and content-encoding headers on their own server (or on any host reached via Req's automatic redirect following). A sub-megabyte response can expand to multiple gigabytes on the victim, crashing the BEAM process. This issue affects req: from 0.1.0 before 0.6.1.

osv:CVE-2026-49755
Complete source record
{
  "id": "a3ed3d360feb05d744ba0d5d399a7ed7023d999615f3858015082448a5ae8104",
  "url": "https://osv.dev/vulnerability/CVE-2026-49755",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Decompression bomb DoS in Req via auto-decoded archive and compressed response bodies",
    "summary": "Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in wojtekmach Req allows attacker-controlled HTTP servers to exhaust memory in a Req client via decompression-bomb response bodies. Req's default response pipeline includes Req.Steps.decode_body/1 and Req.Steps.decompress_body/1 in lib/req/steps.ex. decode_body/1 dispatches on the server-supplied content-type (or URL extension) and calls :zip.extract(body, [:memory]) for application/zip, :erl_tar.extract({:binary, body}, [:memory]) for application/x-tar, and :erl_tar.extract({:binary, body}, [:memory, :compressed]) for application/gzip / .tgz. Each returns the full decompressed archive contents as a [{name, bytes}] list in memory, with no per-entry or total size cap. decompress_body/1 walks the content-encoding header and chains :zlib/:brotli/:ezstd decoders, so a response advertising content-encoding: gzip, gzip, gzip inflates through multiple layers without bound. Both steps are enabled by default, no caller opt-in is required, and the attacker controls the content-type and content-encoding headers on their own server (or on any host reached via Req's automatic redirect following). A sub-megabyte response can expand to multiple gigabytes on the victim, crashing the BEAM process. This issue affects req: from 0.1.0 before 0.6.1.",
    "evidence": "osv:CVE-2026-49755",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-49755",
      "aliases": [
        "CVE-2026-49755",
        "EEF-CVE-2026-49755",
        "GHSA-655f-mp8p-96gv"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "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"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/wojtekmach/req",
              "type": "GIT",
              "events": [
                {
                  "introduced": "ce7113a52efd04012c6f9e8d0b8267439f5fd6b8"
                },
                {
                  "fixed": "36a82523e864739787340604f65ecce26699a0a9"
                },
                {
                  "fixed": "84977e5b1a83f26e749d55ad06e3625464af4e8d"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:wojtekmach:req:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0.1.0"
                      },
                      {
                        "fixed": "0.6.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "84977e5b1a83f26e749d55ad06e3625464af4e8d"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            },
            {
              "repo": "https://github.com/wojtekmach/req.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e37753741cbdc725e6aba3d977b380163bfc0ecb"
                },
                {
                  "fixed": "84977e5b1a83f26e749d55ad06e3625464af4e8d"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "e37753741cbdc725e6aba3d977b380163bfc0ecb"
                      },
                      {
                        "fixed": "84977e5b1a83f26e749d55ad06e3625464af4e8d"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v0.6.0",
            "v0.5.18",
            "v0.5.17",
            "v0.5.16",
            "v0.5.14",
            "v0.5.13",
            "v0.5.12",
            "v0.5.11",
            "v0.5.10",
            "v0.5.9",
            "v0.5.8",
            "v0.5.7",
            "v0.5.6",
            "v0.5.5",
            "v0.5.4",
            "v0.5.3",
            "v0.5.2",
            "v0.5.1",
            "v0.5.0",
            "v0.4.14",
            "v0.4.13",
            "v0.4.12",
            "v0.4.11",
            "v0.4.10",
            "v0.4.9",
            "v0.4.8",
            "v0.4.7",
            "v0.4.6",
            "v0.4.5",
            "v0.4.4",
            "v0.3.11",
            "v0.4.3",
            "v0.4.2",
            "v0.4.1",
            "v0.4.0",
            "v0.3.10",
            "v0.3.9",
            "v0.3.8",
            "v0.3.7",
            "v0.3.6",
            "v0.3.5",
            "v0.3.4",
            "v0.3.3",
            "v0.3.2",
            "v0.3.1",
            "v0.3.0",
            "v0.2.1",
            "v0.2.0",
            "v0.1.1",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-49755.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:33.367779378Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-49755.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-49755",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49755.json",
        "https://github.com/wojtekmach/req/security/advisories/GHSA-655f-mp8p-96gv",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-49755",
        "https://github.com/wojtekmach/req/commit/84977e5b1a83f26e749d55ad06e3625464af4e8d",
        "https://github.com/wojtekmach/req",
        "https://github.com/wojtekmach/req.git"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-409"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49755.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-49755",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 500481,
  "published_at": "2026-06-08T15:20:57.415+00:00"
}