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CVE-2026-88018

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

Published: Sep 10, 2026Updated: Sep 14, 2026 Sources: CVE List NVDCWE-287
9.8CRITICAL
NVD MITRE
EPSS Score
0.5%
Top 59.1%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
Not available

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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:HI:HA:H
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:HConfidentiality
High
I:HIntegrity
High
A:HAvailability
High
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Weaknesses

CWE-287CWE-306

Affected Products

rclone
oss-project
rcloneMixed
Consumer Software / file-utility

Exploitability

Official Patch Available
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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

2 techniques
Initial Access
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References

https://github.com/rclone/rclone/commit/90595f34f27f569be6b27c57fe5ab65057d323bd
github.com
https://github.com/rclone/rclone/releases/tag/v1.75.1
github.com
https://github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c
github.com

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