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CVE-2026-88018— rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass

Quick assessment

Affected
rclone rclone
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

rclone 是一款用于在不同云存储服务商之间同步文件和目录的命令行程序。在版本 1.75.1 之前，当使用 但未配置 的 模式， 允许任意由客户端选择的 accessKeyID 与一个空的 进行配对。随后， 使用相同的空密钥来验证请求的 SigV4 签名，而 会将访问密钥标识符同时作为用户身份和认证值传递给代理，且没有针对每个身份独立的密钥。因此，未经身份验证的网络攻击者可以选择任意的访问密钥，使用空密钥进行签名，并到达该身份对应的 auth-proxy 脚本所解析的后端服务。此问题已在版本 1.75.1 中修复

CVSS 9.8 · Critical
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I. Basic Information for CVE-2026-88018

Vulnerability Information
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Vulnerability Title
rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
认证机制不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
rclone rclone < 1.75.1 -

II. Public POCs for CVE-2026-88018

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III. Intelligence Information for CVE-2026-88018

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Other References for CVE-2026-88018 (2)

Same Patch Batch · rclone · 2026-09-10 · 9 CVEs total

CVE-2026-88044 9.1 CRITICAL rclone: RC per-server auth-proxy bypass
CVE-2026-88045 7.5 HIGH rclone: S3 multipart declared-length memory exhaustion
CVE-2026-88017 7.3 HIGH rclone: FTP cross-session auth-proxy backend confusion
CVE-2026-88016 7.1 HIGH rclone: Directory metadata (chmod/chown/chtimes) applied through a planted symlink in rclo
CVE-2026-88014 6.3 MEDIUM rclone archive/zip: Zip Slip via unsanitized zip entry names lets a malicious archive esca
CVE-2026-88015 5.3 MEDIUM rclone local: crafted Range request against a translated symlink panics (DoS)
CVE-2026-88046 5.3 MEDIUM rclone: source object names can escape the configured root on upload
CVE-2026-88013 3.7 LOW rclone: http backend forwards custom/auth headers to a different host on redirect

IV. Related Vulnerabilities

Same product: rclone
Same vendor: rclone
Same weakness: CWE-287

V. Comments for CVE-2026-88018

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