CVE-2026-88018

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

Published Sep 10, 2026 CVSS 3.1 · 9.8 Critical EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-xwwr-4h3p-r22c rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass
History
Type Values Removed Values Added
CPEs cpe:2.3:a:rclone:rclone:*:*:*:*:*:*:*:*
Type Values Removed Values Added
First Time appeared Rclone
Rclone rclone
Vendors & Products Rclone
Rclone rclone
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description 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.
Title rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass
Weaknesses CWE-287
CWE-306
References
Metrics cvssV3_1

{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Sep 10, 2026, 4:14 PM
Reserved
Sep 9, 2026, 7:19 PM
Status
Analyzed
Published
Sep 10, 2026, 4:18 PM
Modified
Sep 14, 2026, 8:01 PM