rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass (CVE-2026-88018) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-88018

rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass

Answer in brief

CVE-2026-88018 records a Unknown severity vulnerability in rclone serve s3: --auth-proxy without --auth-key authenticates nobody - full SigV4 signature bypass. The current sources do not mark it as known exploited. The current feed maps rclone/rclone (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 10, 2026Updated Sep 10, 2026Source checked Sep 10, 2026First seen by HOL Sep 10, 2026Material review Sep 10, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Not reported

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps rclone/rclone (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
rclone/rclonegeneric	< 1.75.1	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for rclone/rclone.
Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

Published upstream
Sep 10, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 10, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 10, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.