---
title: "CVE-2026-88018: rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass"
url: https://erroneo.us/security/cve/CVE-2026-88018/
description: "CVE-2026-88018 (github.com/rclone/rclone (Go)): rclone is a command-line program to sync files and directories to and from different cloud storage…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-09-10
date_modified: 2026-09-10
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-88018"
kev: false
cvss: 9.8
epss: 0.0051
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.5% , percentile 43: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 43% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes github.com/rclone/rclone (Go) < 1.75.1, fixed in 1.75.1 . Check your lockfile, including transitive dependencies.

## What it is

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

- Go `github.com/rclone/rclone` < 1.75.1 → fixed: 1.75.1

## Affected products (CVE record)

- rclone rclone: < 1.75.1

## Severity

- GitHub_M CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.51% probability of exploitation activity in the next 30 days; percentile 43.

## Sources

- [GitHub Advisory GHSA-xwwr-4h3p-r22c](https://github.com/advisories/GHSA-xwwr-4h3p-r22c)
- [CVE.org record CVE-2026-88018](https://www.cve.org/CVERecord?id=CVE-2026-88018)
- [NVD entry CVE-2026-88018](https://nvd.nist.gov/vuln/detail/CVE-2026-88018)
- [github.com](https://github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c)
- [github.com](https://github.com/rclone/rclone/commit/90595f34f27f569be6b27c57fe5ab65057d323bd)
- [github.com](https://github.com/rclone/rclone/releases/tag/v1.75.1)

---
Source page: https://erroneo.us/security/cve/CVE-2026-88018/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt