Vulnerability-Lookup

GHSA-655F-MP8P-96GV

Vulnerability from github – Published: 2026-07-29 15:23 – Updated: 2026-07-29 15:23

Summary

Req vulnerable to unbounded archive/compression extraction triggered by response content-type

Details

Summary

Req's default response pipeline auto-decodes archive and compressed bodies based on the server-supplied content-type (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by Req.get!/1 can return a tiny "decompression bomb" that expands to many gigabytes on the client and exhausts the BEAM's memory.

Details

1. Archive auto-decoding. Req.Steps.decode_body/1 in lib/req/steps.ex dispatches on the response content-type (or URL extension) and calls Erlang's archive libraries with :memory, returning a [{name, bytes}] list of every entry fully decompressed in RAM: application/zip → :zip.extract(body, [:memory]), application/x-tar → :erl_tar.extract({:binary, body}, [:memory]), application/gzip / .tgz → :erl_tar.extract({:binary, body}, [:memory, :compressed]). No byte cap is enforced before decoding and no per-entry size limit is passed to :zip / :erl_tar.

2. content-encoding chaining. Req.Steps.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.

3. Default-on, attacker-chosen decoder. Both steps are part of Req's default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting content-type and content-encoding on their own server (or on any host reached via Req's automatic redirect following).

PoC

Run an HTTP server that responds 200 with content-type: application/zip and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).
From the victim process, call Req.get!(url) against that server (no special options, no opt-in to archive decoding).
decode_body/1 dispatches on content-type, invokes :zip.extract(body, [:memory]), and the response body becomes [{~c"bomb.bin", <<400 MB of zero bytes>>}]. A sub-MB request produces hundreds of MB resident memory; layering gzip on the content-encoding path or increasing entry size scales arbitrarily.

Impact

Memory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any Req.get!/1 call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.

Severity

8.2 (High)


                  
                    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

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JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Hex",
        "name": "req"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.1.0"
            },
            {
              "fixed": "0.6.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-49755"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-409"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-29T15:23:16Z",
    "nvd_published_at": "2026-06-08T16:16:43Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nReq\u0027s default response pipeline auto-decodes archive and compressed bodies based on the server-supplied `content-type` (or URL extension) and materialises the full decompressed contents in memory with no size cap. An attacker who controls (or can redirect a victim into) an HTTP endpoint reached by `Req.get!/1` can return a tiny \"decompression bomb\" that expands to many gigabytes on the client and exhausts the BEAM\u0027s memory.\n\n### Details\n\n**1. Archive auto-decoding.** `Req.Steps.decode_body/1` in `lib/req/steps.ex` dispatches on the response `content-type` (or URL extension) and calls Erlang\u0027s archive libraries with `:memory`, returning a `[{name, bytes}]` list of every entry fully decompressed in RAM: `application/zip` \u2192 `:zip.extract(body, [:memory])`, `application/x-tar` \u2192 `:erl_tar.extract({:binary, body}, [:memory])`, `application/gzip` / `.tgz` \u2192 `:erl_tar.extract({:binary, body}, [:memory, :compressed])`. No byte cap is enforced before decoding and no per-entry size limit is passed to `:zip` / `:erl_tar`.\n\n**2. content-encoding chaining.** `Req.Steps.decompress_body/1` walks the `content-encoding` header and chains `:zlib` / `:brotli` / `:ezstd` decoders, so a response advertising `content-encoding: gzip, gzip, gzip, \u2026` inflates through multiple layers without bound.\n\n**3. Default-on, attacker-chosen decoder.** Both steps are part of Req\u0027s default pipeline. The caller does not need to opt in, and the attacker chooses which decoder fires by setting `content-type` and `content-encoding` on their own server (or on any host reached via Req\u0027s automatic redirect following).\n\n### PoC\n\n1. Run an HTTP server that responds 200 with `content-type: application/zip` and a body that is a zip archive whose single entry is ~400 MB of zero bytes (compressed wire payload: a few hundred KB).\n2. From the victim process, call `Req.get!(url)` against that server (no special options, no opt-in to archive decoding).\n3. `decode_body/1` dispatches on `content-type`, invokes `:zip.extract(body, [:memory])`, and the response body becomes `[{~c\"bomb.bin\", \u003c\u003c400 MB of zero bytes\u003e\u003e}]`. A sub-MB request produces hundreds of MB resident memory; layering gzip on the `content-encoding` path or increasing entry size scales arbitrarily.\n\n### Impact\n\nMemory-exhaustion denial of service against any Elixir application that uses Req with its default step pipeline to fetch URLs influenced by an untrusted party, including webhook senders, link previews, OAuth/OIDC discovery clients, package mirrors, image proxies, and any `Req.get!/1` call that may follow redirects to attacker-controlled hosts. No authentication is required; a single response can crash the BEAM and take down unrelated workloads on the same VM.",
  "id": "GHSA-655f-mp8p-96gv",
  "modified": "2026-07-29T15:23:16Z",
  "published": "2026-07-29T15:23:16Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/wojtekmach/req/security/advisories/GHSA-655f-mp8p-96gv"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-49755"
    },
    {
      "type": "WEB",
      "url": "https://github.com/wojtekmach/req/commit/84977e5b1a83f26e749d55ad06e3625464af4e8d"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-49755.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/wojtekmach/req"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-49755"
    }
  ],
  "schema_version": "1.4.0",
  "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": "Req vulnerable to unbounded archive/compression extraction triggered by response content-type"
}

CVE-2026-49755 (GCVE-0-2026-49755)

Vulnerability from cvelistv5 – Published: 2026-06-08 15:20 – Updated: 2026-06-08 17:14

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.

Severity

8.2 (High)


                        
                          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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-06-08 16:49 UTC

CWE

CWE-409 - Improper Handling of Highly Compressed Data (Data Amplification)

Assigner

EEF mitre root

References

4 references

URL	Tags
https://github.com/wojtekmach/req/security/adviso…	vendor-advisoryrelated
https://cna.erlef.org/cves/CVE-2026-49755.html	related
https://osv.dev/vulnerability/EEF-CVE-2026-49755	related
https://github.com/wojtekmach/req/commit/84977e5b…	patch

Impacted products

2 products

Vendor	Product	Version
wojtekmach	req	Affected: 0.1.0 , < 0.6.1 (semver) cpe:2.3:a:wojtekmach:req::::::::
wojtekmach	req	Affected: e37753741cbdc725e6aba3d977b380163bfc0ecb , < 84977e5b1a83f26e749d55ad06e3625464af4e8d (git) cpe:2.3:a:wojtekmach:req::::::::

Credits

Peter Ullrich Wojtek Mach Jonatan Männchen / EEF

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-49755",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-08T16:49:57.977214Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-06-08T16:50:03.277Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/wojtekmach/req/security/advisories/GHSA-655f-mp8p-96gv"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "collectionURL": "https://repo.hex.pm",
          "cpes": [
            "cpe:2.3:a:wojtekmach:req:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Req.Steps\u0027"
          ],
          "packageName": "req",
          "packageURL": "pkg:hex/req",
          "product": "req",
          "programFiles": [
            "lib/req/steps.ex"
          ],
          "programRoutines": [
            {
              "name": "\u0027Elixir.Req.Steps\u0027:decode_body/1"
            },
            {
              "name": "\u0027Elixir.Req.Steps\u0027:decompress_body/1"
            }
          ],
          "repo": "https://github.com/wojtekmach/req",
          "vendor": "wojtekmach",
          "versions": [
            {
              "lessThan": "0.6.1",
              "status": "affected",
              "version": "0.1.0",
              "versionType": "semver"
            }
          ]
        },
        {
          "collectionURL": "https://github.com",
          "cpes": [
            "cpe:2.3:a:wojtekmach:req:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Req.Steps\u0027"
          ],
          "packageName": "wojtekmach/req",
          "packageURL": "pkg:github/wojtekmach/req",
          "product": "req",
          "programFiles": [
            "lib/req/steps.ex"
          ],
          "programRoutines": [
            {
              "name": "\u0027Elixir.Req.Steps\u0027:decode_body/1"
            },
            {
              "name": "\u0027Elixir.Req.Steps\u0027:decompress_body/1"
            }
          ],
          "repo": "https://github.com/wojtekmach/req.git",
          "vendor": "wojtekmach",
          "versions": [
            {
              "lessThan": "84977e5b1a83f26e749d55ad06e3625464af4e8d",
              "status": "affected",
              "version": "e37753741cbdc725e6aba3d977b380163bfc0ecb",
              "versionType": "git"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:a:wojtekmach:req:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "0.6.1",
                  "versionStartIncluding": "0.1.0",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ],
          "operator": "AND"
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Peter Ullrich"
        },
        {
          "lang": "en",
          "type": "remediation developer",
          "value": "Wojtek Mach"
        },
        {
          "lang": "en",
          "type": "analyst",
          "value": "Jonatan M\u00e4nnchen / EEF"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "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.\u003cp\u003eReq\u0027s default response pipeline includes \u003ctt\u003e\u0027Elixir.Req.Steps\u0027:decode_body/1\u003c/tt\u003e and \u003ctt\u003e\u0027Elixir.Req.Steps\u0027:decompress_body/1\u003c/tt\u003e in \u003ctt\u003elib/req/steps.ex\u003c/tt\u003e. \u003ctt\u003edecode_body/1\u003c/tt\u003e dispatches on the server-supplied \u003ctt\u003econtent-type\u003c/tt\u003e (or URL extension) and calls \u003ctt\u003e:zip.extract(body, [:memory])\u003c/tt\u003e for \u003ctt\u003eapplication/zip\u003c/tt\u003e, \u003ctt\u003e:erl_tar.extract({:binary, body}, [:memory])\u003c/tt\u003e for \u003ctt\u003eapplication/x-tar\u003c/tt\u003e, and \u003ctt\u003e:erl_tar.extract({:binary, body}, [:memory, :compressed])\u003c/tt\u003e for \u003ctt\u003eapplication/gzip\u003c/tt\u003e / \u003ctt\u003e.tgz\u003c/tt\u003e. Each returns the full decompressed archive contents as a \u003ctt\u003e[{name, bytes}]\u003c/tt\u003e list in memory, with no per-entry or total size cap. \u003ctt\u003edecompress_body/1\u003c/tt\u003e walks the \u003ctt\u003econtent-encoding\u003c/tt\u003e header and chains \u003ctt\u003e:zlib\u003c/tt\u003e/\u003ctt\u003e:brotli\u003c/tt\u003e/\u003ctt\u003e:ezstd\u003c/tt\u003e decoders, so a response advertising \u003ctt\u003econtent-encoding: gzip, gzip, gzip\u003c/tt\u003e inflates through multiple layers without bound.\u003c/p\u003e\u003cp\u003eBoth steps are enabled by default, no caller opt-in is required, and the attacker controls the \u003ctt\u003econtent-type\u003c/tt\u003e and \u003ctt\u003econtent-encoding\u003c/tt\u003e headers on their own server (or on any host reached via Req\u0027s automatic redirect following). A sub-megabyte response can expand to multiple gigabytes on the victim, crashing the BEAM process.\u003c/p\u003e\u003cp\u003eThis issue affects req: from 0.1.0 before 0.6.1.\u003c/p\u003e"
            }
          ],
          "value": "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.\n\nReq\u0027s 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.\n\nBoth 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\u0027s automatic redirect following). A sub-megabyte response can expand to multiple gigabytes on the victim, crashing the BEAM process.\n\nThis issue affects req: from 0.1.0 before 0.6.1."
        }
      ],
      "impacts": [
        {
          "capecId": "CAPEC-197",
          "descriptions": [
            {
              "lang": "en",
              "value": "CAPEC-197 Exponential Data Expansion"
            }
          ]
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 8.2,
            "baseSeverity": "HIGH",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-409",
              "description": "CWE-409 Improper Handling of Highly Compressed Data (Data Amplification)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-08T17:14:08.858Z",
        "orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
        "shortName": "EEF"
      },
      "references": [
        {
          "tags": [
            "vendor-advisory",
            "related"
          ],
          "url": "https://github.com/wojtekmach/req/security/advisories/GHSA-655f-mp8p-96gv"
        },
        {
          "tags": [
            "related"
          ],
          "url": "https://cna.erlef.org/cves/CVE-2026-49755.html"
        },
        {
          "tags": [
            "related"
          ],
          "url": "https://osv.dev/vulnerability/EEF-CVE-2026-49755"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/wojtekmach/req/commit/84977e5b1a83f26e749d55ad06e3625464af4e8d"
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "Decompression bomb DoS in Req via auto-decoded archive and compressed response bodies",
      "workarounds": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "\u003cp\u003eDisable Req\u0027s automatic body decoding on requests that fetch attacker-influenced URLs by passing \u003ctt\u003edecode_body: false\u003c/tt\u003e to \u003ctt\u003e\u0027Elixir.Req\u0027:new/1\u003c/tt\u003e / \u003ctt\u003e\u0027Elixir.Req\u0027:get!/1\u003c/tt\u003e. To also skip the \u003ctt\u003econtent-encoding\u003c/tt\u003e decompression pipeline, pass \u003ctt\u003eraw: true\u003c/tt\u003e. Both options leave the response body as the raw on-the-wire bytes, so the caller can size-check before any decompression.\u003c/p\u003e"
            }
          ],
          "value": "Disable Req\u0027s automatic body decoding on requests that fetch attacker-influenced URLs by passing decode_body: false to Req.new/1 / Req.get!/1. To also skip the content-encoding decompression pipeline, pass raw: true. Both options leave the response body as the raw on-the-wire bytes, so the caller can size-check before any decompression."
        }
      ],
      "x_generator": {
        "engine": "cvelib 1.8.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
    "assignerShortName": "EEF",
    "cveId": "CVE-2026-49755",
    "datePublished": "2026-06-08T15:20:57.415Z",
    "dateReserved": "2026-06-01T13:45:22.448Z",
    "dateUpdated": "2026-06-08T17:14:08.858Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

GHSA-655F-MP8P-96GV

Summary

Details

PoC

Impact

CVE-2026-49755 (GCVE-0-2026-49755)

Tags

Sightings

Nomenclature

Related by attack behaviour