EUVD-2026-75585
GHSA-xwwr-4h3p-r22c
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Unauthenticated remote attacker signs with an empty secret to gain full read/write backend access; the non-default config requirement affects population, not per-attack complexity, so AC:L/PR:N stand.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
5DescriptionCVE.org
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.
AnalysisAI
Authentication bypass in rclone's S3 server mode (rclone serve s3) allows any unauthenticated network attacker to impersonate arbitrary S3 access keys. When rclone serve s3 is started with --auth-proxy but without --auth-key, authPairMiddleware registers whatever accessKeyID the client chooses against an empty s3Secret, and gofakes3 then validates the request's SigV4 signature against that same empty secret - so an attacker can pick any access key, sign with an empty secret, and reach whatever backend the auth-proxy script resolves for that identity. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Requires rclone (prior to 1.75.1) running the 'rclone serve s3' subcommand configured with --auth-proxy AND without --auth-key - this is the exact vulnerable combination named in the advisory. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H = 9.8) is internally consistent with the description: a remote, unauthenticated attacker with low complexity gains full read/write access to backend storage, which is a genuine critical-severity outcome for any exposed instance. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Vendor-released patch: upgrade rclone to version 1.75.1 or later, which requires the auth-proxy to return a non-empty _secret_access_key and refuses the request when it is empty or missing (advisory GHSA-xwwr-4h3p-r22c). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify all rclone deployments configured with 'serve s3' and verify whether both --auth-proxy and --auth-key flags are present; flag configurations lacking --auth-key as critical and immediately isolate or reconfigure with --auth-key parameter. …
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Same weakness CWE-287 – Improper Authentication
View allSame technique Authentication Bypass
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External POC / Exploit Code
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