Vulnerability · Published Sep 10, 2026 · Assigned by GitHub_M
CVE-2026-88018rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass
Critical 9.8
In plain English
A critical-severity improper authentication in rclone from rclone. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 44% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:13 | rclone | no fix listed | DEBIAN-CVE-2026-88018 |
| Go | github.com/rclone/rclone | 1.75.1 | GHSA-xwwr-4h3p-r22c |
| Go | github.com/rclone/rclone | 1.75.1 | GO-2026-6462 |
Affected products (as reported)
Weakness: CWE-287, CWE-306 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
References
- https://github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c x_refsource_CONFIRM
- https://github.com/rclone/rclone/commit/90595f34f27f569be6b27c57fe5ab65057d323bd x_refsource_MISC
- https://github.com/rclone/rclone/releases/tag/v1.75.1 x_refsource_MISC