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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-88018
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-10 16:18:08 UTC
Updated2026-09-10 17:17:08 UTC
Descriptionrclone 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.

Risk And Classification

Primary CVSS: v3.1 9.8 CRITICAL from [email protected]

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

Problem Types: CWE-287 | CWE-306 | CWE-287 CWE-287: Improper Authentication | CWE-306 CWE-306: Missing Authentication for Critical Function

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Rclone Rclone affected < 1.75.1 Not specified

References

ReferenceSourceLinkTags
github.com/rclone/rclone/releases/tag/v1.75.1 [email protected] github.com
github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/rclone/rclone/commit/90595f34f27f569be6b27c57fe5ab65057d323bd [email protected] github.com
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