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Fencer Vulns
critical 9.8

CVE-2026-88018 json

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

published 2026-09-10 59 d ago modified 2026-09-17 52 d ago also BIT-rclone-2026-88018 , EUVD-2026-75585 , GHSA-xwwr-4h3p-r22c , GO-2026-6462

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 43%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/rclone/rclone 1.75.1
  • bitnami rclone 1.75.1
  • rclone rclone 1.75.1
  • govulncheck-vulndb SLES 16.0, SLES for SAP applications 16.0 0.0.20260916T180043-160000.1.1

suse advisories SUSE-SU-2026:23855-1SUSE-SU-2026:23863-1

  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260916T180043-160000.1.1

opensuse advisories openSUSE-SU-2026:21897-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-88018 updated cvss 9.8

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

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
total
Assessed
59 d ago

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 43% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/rclone/rclone/security/advisories/GHSA-xwwr-4h3p-r22c referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
GitHub 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
OSV 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
go github.com/rclone/rclone
<1.75.1
1.75.1
bitnami rclone
<1.75.1
1.75.1

Affected products

  • rclone rclone

Classification

Weakness
  • CWE-287 Improper Authentication
  • CWE-306 Missing Authentication for Critical Functionality

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.