CVE-2026-88018 rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass
An unauthenticated attacker can bypass S3 authentication in rclone serve s3 when using --auth-proxy without --auth-key, gaining unauthorized access to backend storage.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-88018?
CVE-2026-88018 is a critical authentication bypass vulnerability in rclone, published on 10 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Which versions are affected by CVE-2026-88018?
4 open source packages ship an affected version, including github.com/rclone/rclone and rclone. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/rclone/rclone Go | All versions | 1.75.1 |
github.com/rclone/rclone Go | All versions | 1.75.1 |
github.com/rclone/rclone Go | All versions | 1.75.1 |
rclone Bitnami | All versions | 1.75.1 |
Products include Rclone Rclone.
How do I fix CVE-2026-88018?
Upgrade github.com/rclone/rclone to 1.75.1 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-88018 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-88018 exists.
Other vulnerabilities in rclone
- CVE-2026-49980 Rclone: Unauthenticated command execution in `rclone rcd --rc-serve` via inline remote instantiation, bypassing CVE-2026-41179 fix
- CVE-2026-41179 RClone: Unauthenticated operations/fsinfo allows attacker-controlled backend instantiation and local command execution
- CVE-2026-41176 Rclone: Unauthenticated options/set allows runtime auth bypass, leading to sensitive operations and command execution
- CVE-2026-59733 rclone `serve restic --private-repos` authorization bypass: `..` in the URL path lets an authenticated user read, overwrite and delete other users' repositories
- CVE-2026-116191 Rclone before 1.75.2 Path Traversal via serve webdav MKCOL
Sources
Also known as BIT-rclone-2026-88018, DEBIAN-CVE-2026-88018, GHSA-xwwr-4h3p-r22c, GO-2026-6462, MINI-4p3c-74v6-x52g, MINI-8gj4-xc7r-q65x and 7 more.