CVE-2026-88018: rclone Auth Bypass — Fix

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.

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CVSS v3.1 Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS — Exploit Prediction

0.0050

Probability of exploitation

0.42%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-287 Improper Authentication

CWE-306 Missing Authentication

Affected Products

Vendor	Product	Versions
rclone	rclone	< 1.75.1

References

Advisories & Patches

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

Other References

https://github.com/rclone/rclone/releases/tag/v1.75.1

Frequently Asked Questions

What is CVE-2026-88018? +

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. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-88018? +

CVE-2026-88018 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0050, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-88018? +

CVE-2026-88018 affects products from rclone, specifically: rclone. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-88018? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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