# 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.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Sep 2026
- **Updated:** 10 Sep 2026
- **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, MINI-8j37-r3j4-9hmg, MINI-98v9-5v43-2m45, MINI-jv4x-ccwj-jjf8, MINI-mfxj-2xxv-55c7, MINI-q9j3-gjqc-355g, MINI-v979-3c3j-j938, ROOT-APP-GOBINARY-CVE-2026-88018

## 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.

Weakness: CWE-306 (Missing Authentication for Critical Functionality), CWE-287 (Improper Authentication)

## 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 | Ecosystem | 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: Rclone Rclone.

## How do I fix CVE-2026-88018?

Upgrade github.com/rclone/rclone to 1.75.1 or later.

## 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](https://insights.sbomify.com/CVE-2026-49980/): Rclone: Unauthenticated command execution in `rclone rcd --rc-serve` via inline remote instantiation, bypassing CVE-2026-41179 fix (critical 9.8)
- [CVE-2026-41179](https://insights.sbomify.com/CVE-2026-41179/): RClone: Unauthenticated operations/fsinfo allows attacker-controlled backend instantiation and local command execution (critical 9.2)
- [CVE-2026-41176](https://insights.sbomify.com/CVE-2026-41176/): Rclone: Unauthenticated options/set allows runtime auth bypass, leading to sensitive operations and command execution (critical 9.2)
- [CVE-2026-59733](https://insights.sbomify.com/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 (high 8.8)
- [CVE-2026-116191](https://insights.sbomify.com/CVE-2026-116191/): Rclone before 1.75.2 Path Traversal via serve webdav MKCOL (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-88018 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-88018 exists.

Affected packages and fixed versions:
- github.com/rclone/rclone (Go): affected all versions; fixed in 1.75.1
- github.com/rclone/rclone (Go): affected all versions; fixed in 1.75.1
- github.com/rclone/rclone (Go): affected all versions; fixed in 1.75.1
- rclone (Bitnami): affected all versions; fixed in 1.75.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-88018/ (Markdown: https://insights.sbomify.com/CVE-2026-88018/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-88018
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-88018
- OSV: https://osv.dev/vulnerability/CVE-2026-88018

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-88018/
Summaries are generated and may contain mistakes; the official description above is the record.