Vulnerability-Lookup

CVE-2026-32688 (GCVE-0-2026-32688)

Vulnerability from cvelistv5 – Published: 2026-04-27 13:45 – Updated: 2026-04-29 17:08

Title

Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy

Summary

Allocation of Resources Without Limits or Throttling vulnerability in elixir-plug plug_cowboy allows unauthenticated remote denial of service via atom table exhaustion. Plug.Cowboy.Conn.conn/1 in lib/plug/cowboy/conn.ex calls String.to_atom/1 on the value returned by :cowboy_req.scheme/1. For HTTP/2 connections, cowlib passes the client-supplied :scheme pseudo-header value through verbatim without validation. Each unique value permanently allocates a new entry in the BEAM atom table. Since atoms are never garbage-collected and the atom table has a fixed limit (default 1,048,576), an unauthenticated attacker can exhaust the table by sending HTTP/2 requests with unique :scheme values, causing the Erlang VM to abort with system_limit and taking down the entire node. This vulnerability does not affect HTTP/1.1, where cowboy derives the scheme from the listener type rather than from a client-supplied header. This issue affects plug_cowboy: from 2.0.0 before 2.8.1.

Severity

8.7 (High)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-04-27 19:04 UTC

CWE

CWE-770 - Allocation of Resources Without Limits or Throttling

Assigner

EEF CNA under the mitre root

CNA scorecard A 97/100 over 314 records in the last 180 days details

References

4 references

URL	Tags
https://github.com/elixir-plug/plug_cowboy/securi…	vendor-advisoryrelated
https://cna.erlef.org/cves/CVE-2026-32688.html	related
https://osv.dev/vulnerability/EEF-CVE-2026-32688	related
https://github.com/elixir-plug/plug_cowboy/commit…	patch

Impacted products

2 products

Vendor	Product	Version	CPE status
elixir-plug	plug_cowboy	Affected: 2.0.0 , < 2.8.1 (semver) cpe:2.3:a:elixir-plug:plug_cowboy::::::::
elixir-plug	plug_cowboy	Affected: 12ecfd024bb179d48b018fecf074e43fe6a19c83 , < bfb34cb45eb354e56437f7023fb306de1bf9c19b (git) cpe:2.3:a:elixir-plug:plug_cowboy::::::::

Credits

Peter Ullrich

Show details on NVD website

JSON

To clipboard

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              "versions": [
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                      "criteria": "cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*",
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                      "vulnerable": true
                    }
                  ],
                  "negate": false,
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                }
              ],
              "operator": "AND"
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          ],
          "credits": [
            {
              "lang": "en",
              "type": "finder",
              "value": "Peter Ullrich"
            }
          ],
          "descriptions": [
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              "lang": "en",
              "supportingMedia": [
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                  "base64": false,
                  "type": "text/html",
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                }
              ],
              "value": "Allocation of Resources Without Limits or Throttling vulnerability in elixir-plug plug_cowboy allows unauthenticated remote denial of service via atom table exhaustion.\n\nPlug.Cowboy.Conn.conn/1 in lib/plug/cowboy/conn.ex calls String.to_atom/1 on the value returned by :cowboy_req.scheme/1. For HTTP/2 connections, cowlib passes the client-supplied :scheme pseudo-header value through verbatim without validation. Each unique value permanently allocates a new entry in the BEAM atom table. Since atoms are never garbage-collected and the atom table has a fixed limit (default 1,048,576), an unauthenticated attacker can exhaust the table by sending HTTP/2 requests with unique :scheme values, causing the Erlang VM to abort with system_limit and taking down the entire node.\n\nThis vulnerability does not affect HTTP/1.1, where cowboy derives the scheme from the listener type rather than from a client-supplied header.\n\nThis issue affects plug_cowboy: from 2.0.0 before 2.8.1."
            }
          ],
          "impacts": [
            {
              "capecId": "CAPEC-125",
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                  "value": "CAPEC-125 Flooding"
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          ],
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                "attackVector": "NETWORK",
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                "privilegesRequired": "NONE",
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                "subConfidentialityImpact": "NONE",
                "subIntegrityImpact": "NONE",
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                "valueDensity": "NOT_DEFINED",
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                "vulnerabilityResponseEffort": "NOT_DEFINED"
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          "problemTypes": [
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          "providerMetadata": {
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          },
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              "tags": [
                "related"
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              "url": "https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b"
            }
          ],
          "source": {
            "discovery": "EXTERNAL"
          },
          "title": "Atom table exhaustion via HTTP/2 :scheme pseudo-header in plug_cowboy",
          "workarounds": [
            {
              "lang": "en",
              "supportingMedia": [
                {
                  "base64": false,
                  "type": "text/html",
                  "value": "Disable HTTP/2 on the \u003ctt\u003ePlug.Cowboy.https/3\u003c/tt\u003e listener by passing \u003ctt\u003eprotocol_options: %{protocols: [:http]}\u003c/tt\u003e in the cowboy options. This restricts the listener to HTTP/1.1, where the scheme is derived from the listener type and is not attacker-controlled."
                }
              ],
              "value": "Disable HTTP/2 on the Plug.Cowboy.https/3 listener by passing protocol_options: %{protocols: [:http]} in the cowboy options. This restricts the listener to HTTP/1.1, where the scheme is derived from the listener type and is not attacker-controlled."
            }
          ],
          "x_generator": {
            "engine": "cvelib 1.8.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
        "assignerShortName": "EEF",
        "cveId": "CVE-2026-32688",
        "datePublished": "2026-04-27T13:45:35.160Z",
        "dateReserved": "2026-03-13T09:12:14.475Z",
        "dateUpdated": "2026-04-28T04:25:01.084Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}

FKIE_CVE-2026-32688

Vulnerability from fkie_nvd - Published: 2026-04-27 14:16 - Updated: 2026-06-17 10:36

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

URL	Tags
6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://cna.erlef.org/cves/CVE-2026-32688.html	Third Party Advisory
6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b	Patch
6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2	Vendor Advisory
6b3ad84c-e1a6-4bf7-a703-f496b71e49db	https://osv.dev/vulnerability/EEF-CVE-2026-32688	Third Party Advisory

Impacted products

	Vendor	Product	Version
	elixir-plug	plug.cowboy	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "collectionURL": "https://repo.hex.pm",
          "cpes": [
            "cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Plug.Cowboy.Conn\u0027"
          ],
          "packageName": "plug_cowboy",
          "packageURL": "pkg:hex/plug_cowboy",
          "product": "plug_cowboy",
          "programFiles": [
            "lib/plug/cowboy/conn.ex"
          ],
          "programRoutines": [
            {
              "name": "\u0027Elixir.Plug.Cowboy.Conn\u0027:conn/1"
            }
          ],
          "repo": "https://github.com/elixir-plug/plug_cowboy",
          "vendor": "elixir-plug",
          "versions": [
            {
              "lessThan": "2.8.1",
              "status": "affected",
              "version": "2.0.0",
              "versionType": "semver"
            }
          ]
        },
        {
          "collectionURL": "https://github.com",
          "cpes": [
            "cpe:2.3:a:elixir-plug:plug_cowboy:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "unaffected",
          "modules": [
            "\u0027Elixir.Plug.Cowboy.Conn\u0027"
          ],
          "packageName": "elixir-plug/plug_cowboy",
          "packageURL": "pkg:github/elixir-plug/plug_cowboy",
          "product": "plug_cowboy",
          "programFiles": [
            "lib/plug/cowboy/conn.ex"
          ],
          "programRoutines": [
            {
              "name": "\u0027Elixir.Plug.Cowboy.Conn\u0027:conn/1"
            }
          ],
          "repo": "https://github.com/elixir-plug/plug_cowboy",
          "vendor": "elixir-plug",
          "versions": [
            {
              "lessThan": "bfb34cb45eb354e56437f7023fb306de1bf9c19b",
              "status": "affected",
              "version": "12ecfd024bb179d48b018fecf074e43fe6a19c83",
              "versionType": "git"
            }
          ]
        }
      ],
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:elixir-plug:plug.cowboy:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "D18EA080-8E40-4503-AA95-54EF882FE1D7",
              "versionEndExcluding": "2.8.1",
              "versionStartIncluding": "2.0.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Allocation of Resources Without Limits or Throttling vulnerability in elixir-plug plug_cowboy allows unauthenticated remote denial of service via atom table exhaustion.\n\nPlug.Cowboy.Conn.conn/1 in lib/plug/cowboy/conn.ex calls String.to_atom/1 on the value returned by :cowboy_req.scheme/1. For HTTP/2 connections, cowlib passes the client-supplied :scheme pseudo-header value through verbatim without validation. Each unique value permanently allocates a new entry in the BEAM atom table. Since atoms are never garbage-collected and the atom table has a fixed limit (default 1,048,576), an unauthenticated attacker can exhaust the table by sending HTTP/2 requests with unique :scheme values, causing the Erlang VM to abort with system_limit and taking down the entire node.\n\nThis vulnerability does not affect HTTP/1.1, where cowboy derives the scheme from the listener type rather than from a client-supplied header.\n\nThis issue affects plug_cowboy: from 2.0.0 before 2.8.1."
    }
  ],
  "id": "CVE-2026-32688",
  "lastModified": "2026-06-17T10:36:12.470",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 8.7,
          "baseSeverity": "HIGH",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "HIGH",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-32688",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-04-27T19:04:33.154446Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-04-27T14:16:47.340",
  "references": [
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://cna.erlef.org/cves/CVE-2026-32688.html"
    },
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b"
    },
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "tags": [
        "Vendor Advisory"
      ],
      "url": "https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2"
    },
    {
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-32688"
    }
  ],
  "sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-770"
        }
      ],
      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
      "type": "Secondary"
    }
  ]
}

GHSA-Q8X4-X7MP-5VG2

Vulnerability from github – Published: 2026-05-05 21:46 – Updated: 2026-05-05 21:46

Summary

Plug.Cowboy vulnerable to unauthenticated remote DoS via HTTP/2 `:scheme` atom-table exhaustion

Details

Summary

An unauthenticated remote denial-of-service vulnerability in Plug.Cowboy.Conn allows any attacker who can reach an HTTPS Plug.Cowboy listener via HTTP/2 to permanently exhaust the BEAM atom table and crash the entire Erlang VM.

Am I Affected?

All users running plug_cowboy with HTTP/2 may be affected, this includes Phoenix applications. If another HTTP adapter such as Bandit is used, then the consuming project is not affected. If the HTTP/2 endpoint is exposed directly (without a proxy) then the project will be affected. If a proxy is in use then it depends on the proxy configuration. Many proxies use HTTP/1.1 internally, and would be unaffected.

Impact

The vulnerability will allow crashing the Erlang VM (BEAM) via atom exhaustion.

Mitigation

Users are advised to update to plug_cowboy v2.8.1 to mitigate this issue.

Credits

Plug.Cowboy thanks Peter Ullrich for finding and responsibly disclosing this vulnerability.

Severity

8.7 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Hex",
        "name": "plug_cowboy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "2.8.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-32688"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-05T21:46:09Z",
    "nvd_published_at": "2026-04-27T14:16:47Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\nAn unauthenticated remote denial-of-service vulnerability in `Plug.Cowboy.Conn` allows any attacker who can reach an HTTPS Plug.Cowboy listener via HTTP/2 to permanently exhaust the BEAM atom table and crash the entire Erlang VM.\n\n## Am I Affected?\n\nAll users running plug_cowboy with HTTP/2 may be affected, this includes Phoenix applications. If another HTTP adapter such as Bandit is used, then the consuming project is not affected. If the HTTP/2 endpoint is exposed directly (without a proxy) then the project will be affected. If a proxy is in use then it depends on the proxy configuration. Many proxies use HTTP/1.1 internally, and would be unaffected.\n\n## Impact\n\nThe vulnerability will allow crashing the Erlang VM (BEAM) via atom exhaustion.\n\n## Mitigation\n\nUsers are advised to update to plug_cowboy v2.8.1 to mitigate this issue.\n\n## Credits\nPlug.Cowboy thanks Peter Ullrich for finding and responsibly disclosing this vulnerability.",
  "id": "GHSA-q8x4-x7mp-5vg2",
  "modified": "2026-05-05T21:46:09Z",
  "published": "2026-05-05T21:46:09Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/elixir-plug/plug_cowboy/security/advisories/GHSA-q8x4-x7mp-5vg2"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-32688"
    },
    {
      "type": "WEB",
      "url": "https://github.com/elixir-plug/plug_cowboy/commit/bfb34cb45eb354e56437f7023fb306de1bf9c19b"
    },
    {
      "type": "WEB",
      "url": "https://cna.erlef.org/cves/CVE-2026-32688.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/elixir-plug/plug_cowboy"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/EEF-CVE-2026-32688"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Plug.Cowboy vulnerable to unauthenticated remote DoS via HTTP/2 `:scheme` atom-table exhaustion"
}

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.

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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.
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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.

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CVE-2026-32688 (GCVE-0-2026-32688)

FKIE_CVE-2026-32688

GHSA-Q8X4-X7MP-5VG2

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