Vulnerability-Lookup

CVE-2026-88018 (GCVE-0-2026-88018)

Vulnerability from cvelistv5 – Published: 2026-09-10 16:03 – Updated: 2026-09-10 16:14

Title

rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass

Summary

rclone is a command-line program to sync files and directories to and from different cloud storage providers. Prior to 1.75.1, rclone serve s3 configured with --auth-proxy but without --auth-key allows authPairMiddleware to register any client-chosen accessKeyID with an empty ws.s3Secret. gofakes3 then verifies the request’s SigV4 signature against that same empty secret, while Server.auth passes the access key identifier as both the user and authentication value to the proxy without an independent per-identity secret. An unauthenticated network attacker can therefore choose an arbitrary access key, sign with an empty secret, and reach whatever backend the auth-proxy script resolves for that identity. This issue is fixed in version 1.75.1.

Severity

9.8 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

SSVC

Exploitation: poc Automatable: yes Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-10 16:14 UTC

CWE

CWE-287 - Improper Authentication
CWE-306 - Missing Authentication for Critical Function

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/rclone/rclone/security/advisor…	x_refsource_CONFIRM
https://github.com/rclone/rclone/commit/90595f34f…	x_refsource_MISC
https://github.com/rclone/rclone/releases/tag/v1.75.1	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
rclone	rclone	Affected: < 1.75.1	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-88018

Vulnerability from fkie_nvd - Published: 2026-09-10 16:18 - Updated: 2026-09-10 19:54

Severity

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

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/rclone/rclone/commit/90595f34f27f569be6b27c57fe5ab65057d323bd
	security-advisories@github.com	https://github.com/rclone/rclone/releases/tag/v1.75.1
	security-advisories@github.com	https://github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "rclone",
          "vendor": "rclone",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.75.1"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
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    {
      "lang": "en",
      "value": "rclone is a command-line program to sync files and directories to and from different cloud storage providers. Prior to 1.75.1, rclone serve s3 configured with --auth-proxy but without --auth-key allows authPairMiddleware to register any client-chosen accessKeyID with an empty ws.s3Secret. gofakes3 then verifies the request\u2019s SigV4 signature against that same empty secret, while Server.auth passes the access key identifier as both the user and authentication value to the proxy without an independent per-identity secret. An unauthenticated network attacker can therefore choose an arbitrary access key, sign with an empty secret, and reach whatever backend the auth-proxy script resolves for that identity. This issue is fixed in version 1.75.1."
    }
  ],
  "id": "CVE-2026-88018",
  "lastModified": "2026-09-10T19:54:25.810",
  "metrics": {
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        "cvssData": {
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GHSA-XWWR-4H3P-R22C

Vulnerability from github – Published: 2026-09-10 22:49 – Updated: 2026-09-10 22:49

Summary

rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass

Details

Summary

rclone serve s3's handler chain, when --auth-proxy is configured, is (outermost first): authPairMiddleware -> proxyAuthMiddleware -> gofakes3's own SigV4-verifying handler.

authPairMiddleware parses the accessKeyID straight out of the incoming request's own Authorization header (entirely client-controlled) and registers {accessKey: ws.s3Secret} into gofakes3's shared credential store via AddAuthKeys, for EVERY access key any client presents - not just ones previously known to the server. ws.s3Secret defaults to "" whenever --auth-key is not set, which the --auth-proxy documentation (and the reference bin/test_proxy.py) presents as a complete, standalone authentication mechanism requiring no other flag - matching how it's used for serve webdav/ftp/sftp.

gofakes3's SigV4 verification then checks the request's signature against exactly the secret authPairMiddleware just registered for that same client-chosen key. An empty string is a valid HMAC key, so a caller can trivially compute a correct SigV4 signature for ANY access key ID of their choosing using an empty secret, and verification passes.

Crucially, the auth-proxy script never receives a real secret to verify against, for S3 specifically: Server.auth() calls w.proxy.Call(md5(accessKeyID), accessKeyID, false, r.RemoteAddr) - passing the access key ID itself as BOTH the hashed "user" and the raw "auth"/password fields. Contrast with serve webdav/ftp/sftp, whose proxy integration passes the client's actual typed password (see bin/test_proxy.py, which forwards it into a backing SFTP login for real verification). For S3, no independent secret is ever transmitted to the proxy script at all, so no script - however carefully written - can distinguish a legitimate holder of an access key ID from an attacker who merely picked the same string.

Net effect: with --auth-proxy configured and --auth-key not also set (the configuration the feature is documented to support standalone), SigV4 signature verification authenticates nobody.

Details

Vulnerable code (before fix):

func authPairMiddleware(next http.Handler, ws *Server) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        accessKey, _ := parseAccessKeyID(r)
        authPair := map[string]string{accessKey: ws.s3Secret}
        ws.faker.AddAuthKeys(authPair)
        next.ServeHTTP(w, r)
    })
}

PoC

Built and signed a request by hand (via the vendored github.com/aws/aws-sdk-go-v2/aws/signer/v4) using a freshly-random access key ID never configured or returned by anything, with SecretAccessKey: "", against a real rclone serve s3 --auth-proxy <script> instance with no --auth-key set:

status=200
<ListAllMyBucketsResult>...<Bucket><Name>mybucket</Name>...

A fully authenticated, successful bucket listing, with zero prior credential knowledge.

Impact

Any network-reachable, unauthenticated attacker who knows (or discovers) that a target is running rclone serve s3 --auth-proxy without --auth-key can choose an arbitrary access key ID, sign a request against an empty secret, and be treated as an authenticated user by the auth-proxy script - reaching whatever backend that script resolves the chosen identity to. No credentials, prior access, or user interaction of any kind are required.

Fix

Refuse to start rclone serve s3 when --auth-proxy is set without --auth-key, rather than silently falling back to a signature check that authenticates nobody:

if proxyOpt.AuthProxy != "" && len(opt.AuthKey) == 0 {
    return nil, errors.New("serve s3: --auth-proxy requires --auth-key to also be set (SigV4 has no other way to verify a signature for a dynamically-proxied identity)")
}

Note this is a minimal fix for the zero-knowledge bypass; once --auth-key is also set, every access key ID still shares that one static secret for signature-verification purposes (a caller who knows it can request any identity from the proxy script) - a narrower, pre-existing limitation flagged for awareness but not changed here, since a complete fix needs the auth-proxy wire protocol to carry a per-identity secret for S3 specifically (a larger design change).

Severity

9.8 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/rclone/rclone"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.75.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-88018"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-287",
      "CWE-306"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-10T22:49:07Z",
    "nvd_published_at": "2026-09-10T16:18:08Z",
    "severity": "CRITICAL"
  },
  "details": "### Summary\n`rclone serve s3`\u0027s handler chain, when `--auth-proxy` is configured, is (outermost first): `authPairMiddleware` -\u003e `proxyAuthMiddleware` -\u003e gofakes3\u0027s own SigV4-verifying handler.\n\n`authPairMiddleware` parses the accessKeyID straight out of the incoming request\u0027s own `Authorization` header (entirely client-controlled) and registers `{accessKey: ws.s3Secret}` into gofakes3\u0027s shared credential store via `AddAuthKeys`, for EVERY access key any client presents - not just ones previously known to the server. `ws.s3Secret` defaults to `\"\"` whenever `--auth-key` is not set, which the `--auth-proxy` documentation (and the reference `bin/test_proxy.py`) presents as a complete, standalone authentication mechanism requiring no other flag - matching how it\u0027s used for `serve webdav`/`ftp`/`sftp`.\n\ngofakes3\u0027s SigV4 verification then checks the request\u0027s signature against exactly the secret `authPairMiddleware` just registered for that same client-chosen key. An empty string is a valid HMAC key, so a caller can trivially compute a correct SigV4 signature for ANY access key ID of their choosing using an empty secret, and verification passes.\n\nCrucially, the auth-proxy script never receives a real secret to verify against, for S3 specifically: `Server.auth()` calls `w.proxy.Call(md5(accessKeyID), accessKeyID, false, r.RemoteAddr)` - passing the access key ID itself as BOTH the hashed \"user\" and the raw \"auth\"/password fields. Contrast with `serve webdav`/`ftp`/`sftp`, whose proxy integration passes the client\u0027s actual typed password (see `bin/test_proxy.py`, which forwards it into a backing SFTP login for real verification). For S3, no independent secret is ever transmitted to the proxy script at all, so no script - however carefully written - can distinguish a legitimate holder of an access key ID from an attacker who merely picked the same string.\n\nNet effect: with `--auth-proxy` configured and `--auth-key` not also set (the configuration the feature is documented to support standalone), SigV4 signature verification authenticates nobody.\n\n### Details\nVulnerable code (before fix):\n```go\nfunc authPairMiddleware(next http.Handler, ws *Server) http.Handler {\n\treturn http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {\n\t\taccessKey, _ := parseAccessKeyID(r)\n\t\tauthPair := map[string]string{accessKey: ws.s3Secret}\n\t\tws.faker.AddAuthKeys(authPair)\n\t\tnext.ServeHTTP(w, r)\n\t})\n}\n```\n\n### PoC\nBuilt and signed a request by hand (via the vendored `github.com/aws/aws-sdk-go-v2/aws/signer/v4`) using a freshly-random access key ID never configured or returned by anything, with `SecretAccessKey: \"\"`, against a real `rclone serve s3 --auth-proxy \u003cscript\u003e` instance with no `--auth-key` set:\n```\nstatus=200\n\u003cListAllMyBucketsResult\u003e...\u003cBucket\u003e\u003cName\u003emybucket\u003c/Name\u003e...\n```\nA fully authenticated, successful bucket listing, with zero prior credential knowledge.\n\n### Impact\nAny network-reachable, unauthenticated attacker who knows (or discovers) that a target is running `rclone serve s3 --auth-proxy` without `--auth-key` can choose an arbitrary access key ID, sign a request against an empty secret, and be treated as an authenticated user by the auth-proxy script - reaching whatever backend that script resolves the chosen identity to. No credentials, prior access, or user interaction of any kind are required.\n\n### Fix\nRefuse to start `rclone serve s3` when `--auth-proxy` is set without `--auth-key`, rather than silently falling back to a signature check that authenticates nobody:\n```go\nif proxyOpt.AuthProxy != \"\" \u0026\u0026 len(opt.AuthKey) == 0 {\n\treturn nil, errors.New(\"serve s3: --auth-proxy requires --auth-key to also be set (SigV4 has no other way to verify a signature for a dynamically-proxied identity)\")\n}\n```\nNote this is a minimal fix for the zero-knowledge bypass; once `--auth-key` is also set, every access key ID still shares that one static secret for signature-verification purposes (a caller who knows it can request any identity from the proxy script) - a narrower, pre-existing limitation flagged for awareness but not changed here, since a complete fix needs the auth-proxy wire protocol to carry a per-identity secret for S3 specifically (a larger design change).",
  "id": "GHSA-xwwr-4h3p-r22c",
  "modified": "2026-09-10T22:49:07Z",
  "published": "2026-09-10T22:49:07Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-88018"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rclone/rclone/commit/90595f34f27f569be6b27c57fe5ab65057d323bd"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/rclone/rclone"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rclone/rclone/releases/tag/v1.75.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass"
}

ubuntu-cve-2026-88018

Vulnerability from osv_ubuntu

Published

2026-09-11 00:00

Modified

2026-09-11 00:00

Summary

Details

(rclone is a command-line program to sync files and directories to and ...)

Severity

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-88018	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-88018	REPORT
	https://github.com/rclone/rclone/security/advisor…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-ncw-rclone-dev",
            "binary_version": "1.36-3ubuntu0.2"
          },
          {
            "binary_name": "rclone",
            "binary_version": "1.36-3ubuntu0.2"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:18.04:LTS",
        "name": "rclone",
        "purl": "pkg:deb/ubuntu/rclone@1.36-3ubuntu0.2?arch=source\u0026distro=bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.36-3",
        "1.36-3ubuntu0.1",
        "1.36-3ubuntu0.2"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-rclone-rclone-dev",
            "binary_version": "1.50.2-2ubuntu0.2+esm1"
          },
          {
            "binary_name": "rclone",
            "binary_version": "1.50.2-2ubuntu0.2+esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:20.04:LTS",
        "name": "rclone",
        "purl": "pkg:deb/ubuntu/rclone@1.50.2-2ubuntu0.2+esm1?arch=source\u0026distro=esm-apps/focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.47.0+ex1-6",
        "1.47.0+ex1-7",
        "1.49.5-2",
        "1.49.5-3",
        "1.50.2-2",
        "1.50.2-2ubuntu0.1",
        "1.50.2-2ubuntu0.2",
        "1.50.2-2ubuntu0.2+esm1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-rclone-rclone-dev",
            "binary_version": "1.53.3-4ubuntu1.22.04.5+esm1"
          },
          {
            "binary_name": "rclone",
            "binary_version": "1.53.3-4ubuntu1.22.04.5+esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:22.04:LTS",
        "name": "rclone",
        "purl": "pkg:deb/ubuntu/rclone@1.53.3-4ubuntu1.22.04.5+esm1?arch=source\u0026distro=esm-apps/jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.53.3-1",
        "1.53.3-2",
        "1.53.3-4",
        "1.53.3-4ubuntu1",
        "1.53.3-4ubuntu1.22.04.1",
        "1.53.3-4ubuntu1.22.04.2",
        "1.53.3-4ubuntu1.22.04.3",
        "1.53.3-4ubuntu1.22.04.3+esm1",
        "1.53.3-4ubuntu1.22.04.4",
        "1.53.3-4ubuntu1.22.04.4+esm1",
        "1.53.3-4ubuntu1.22.04.5",
        "1.53.3-4ubuntu1.22.04.5+esm1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-rclone-rclone-dev",
            "binary_version": "1.60.1+dfsg-3ubuntu0.24.04.6+esm1"
          },
          {
            "binary_name": "rclone",
            "binary_version": "1.60.1+dfsg-3ubuntu0.24.04.6+esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:24.04:LTS",
        "name": "rclone",
        "purl": "pkg:deb/ubuntu/rclone@1.60.1+dfsg-3ubuntu0.24.04.6+esm1?arch=source\u0026distro=esm-apps/noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.60.1+dfsg-2build1",
        "1.60.1+dfsg-3",
        "1.60.1+dfsg-3ubuntu0.24.04.1",
        "1.60.1+dfsg-3ubuntu0.24.04.2",
        "1.60.1+dfsg-3ubuntu0.24.04.3",
        "1.60.1+dfsg-3ubuntu0.24.04.4",
        "1.60.1+dfsg-3ubuntu0.24.04.4+esm1",
        "1.60.1+dfsg-3ubuntu0.24.04.5",
        "1.60.1+dfsg-3ubuntu0.24.04.5+esm1",
        "1.60.1+dfsg-3ubuntu0.24.04.6",
        "1.60.1+dfsg-3ubuntu0.24.04.6+esm1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "golang-github-rclone-rclone-dev",
            "binary_version": "1.60.1+dfsg-4ubuntu3.2+esm1"
          },
          {
            "binary_name": "rclone",
            "binary_version": "1.60.1+dfsg-4ubuntu3.2+esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:26.04:LTS",
        "name": "rclone",
        "purl": "pkg:deb/ubuntu/rclone@1.60.1+dfsg-4ubuntu3.2+esm1?arch=source\u0026distro=esm-apps/resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.60.1+dfsg-4ubuntu2",
        "1.60.1+dfsg-4ubuntu3",
        "1.60.1+dfsg-4ubuntu3.1",
        "1.60.1+dfsg-4ubuntu3.1+esm1",
        "1.60.1+dfsg-4ubuntu3.2",
        "1.60.1+dfsg-4ubuntu3.2+esm1"
      ]
    }
  ],
  "aliases": [],
  "details": "(rclone is a command-line program to sync files and directories to and ...)",
  "id": "UBUNTU-CVE-2026-88018",
  "modified": "2026-09-11T00:00:00Z",
  "published": "2026-09-11T00:00:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-88018"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-88018"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-88018"
  ]
}

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.

Action not permitted

CVE-2026-88018 (GCVE-0-2026-88018)

FKIE_CVE-2026-88018

GHSA-XWWR-4H3P-R22C

Summary

Details

PoC

Impact

Fix

ubuntu-cve-2026-88018

Vulnerability from osv_ubuntu

Tags

Sightings

Nomenclature