CVE-2026-88017: rclone FTP cross-session auth-proxy backend confusion

CVE-2026-88017 · Severity: high · CVSS 7.3 · Published 2026-09-10

rclone's FTP server with auth-proxy support stores authenticated user credentials in a server-wide map keyed only by username, without binding them to individual FTP sessions. When two users with different credentials share the same username and have access to different backend storage locations, an authenticated attacker can gain unauthorized read, write, and delete access to another user's data by keeping their session open while a victim logs in, causing the attacker's session to be silently redirected to the victim's backend.

Technologies: github.com/rclone/rclone (Go), Rclone. Vendors: Go, Rclone.

Quick answers

Is CVE-2026-88017 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-88017 being exploited in the wild.
How severe is CVE-2026-88017?
High severity, with a CVSS score of 7.3, published 10 September 2026.
Which products and versions are affected?
github.com/rclone/rclone (Go) >= 1.64.0, <= 1.75.0, SEMVER:introduced=1.64.0,fixed=1.75.1; Rclone >=1.64.0, <=1.75.0.
Is there a fix for CVE-2026-88017?
Yes. github.com/rclone/rclone (Go): upgrade to 1.75.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-88017 attacked?
It is attacked over the network, in a hosted service.
Am I affected by CVE-2026-88017?
Check whether you run github.com/rclone/rclone (Go) or Rclone at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • github.com/rclone/rclone (Go): upgrade to 1.75.1 or later
    go get github.com/rclone/rclone@v1.75.1

Technical details

The vulnerability is a session-isolation failure in rclone's FTP auth-proxy driver. When a user authenticates via FTP, the driver stores an obscured password in a driver-global map keyed only by username (cmd/serve/ftp/ftp.go:170-178), discarding the returned VFS and cache key from the authentication call. For each subsequent FTP operation, the driver retrieves whichever password was most recently stored for that username and calls the proxy again, rather than maintaining per-session authentication state. If two different credentials use the same username but resolve to different backend locations (a supported deployment model per cmd/serve/proxy:235-243), a later login overwrites the map entry. The first session's subsequent operations then execute against the second user's backend using the second user's credentials, without re-authentication. The attack requires: (1) an auth-proxy that accepts distinct credentials for the same username with different backend authority, (2) the attacker to maintain an active FTP session while a victim with a different credential logs in with the same username, and (3) the attacker to issue additional FTP commands after the victim's login. A mutex prevents data races but does not provide session isolation. Patch available in v1.75.1.

Affected products

  • rclone rclone >=1.64.0, <=1.75.0

Identifiers

  • CVE-2026-88017
  • GHSA-c476-6w5q-jw77
  • GO-2026-6458

Timeline

  • 2026-09-04: disclosed
  • 2026-09-10: patched: patch released in v1.75.1
  • 2026-09-10: advisory

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.