Security Digest · Vulnerability record
CVE-2026-88044: rclone: RC per-server auth-proxy bypass
rclone is a command-line program to sync files and directories to and from different cloud storage providers.
CVSS 9.1 Critical EPSS 0.5% · p41
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.5%, percentile 41: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 41% 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) >= 1.70.0, < 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. From 1.70.0 until 1.75.1, the serve/start RC interface accepts per-server proxyOpt.AuthProxy settings, and the FTP and S3 constructors in cmd/serve/ftp/ftp.go and cmd/serve/s3/server.go incorrectly check the process-global proxy.Opt.AuthProxy value instead. When the global value is empty, the request-local authentication proxy is ignored: FTP falls back to the fixed filesystem with username anonymous and any password, while S3 with AuthKey serves the fixed RC fs rather than the backend selected by the proxy. The dedicated command-line servers that configure the global option are not affected. This issue is fixed in version 1.75.1.
From the GitHub advisory
Summary
serve/start accepts protocol options in a per-server proxyOpt object. The FTP and S3 RC adapters parse that object and pass it to their server constructors, but the constructors decide whether proxy authentication is enabled by checking the process-global proxy.Opt.AuthProxy instead of the supplied proxyOpt.AuthProxy.
When the process-global option is empty—the normal case when only the RC request configures the server—the supplied authentication proxy is silently ignored. FTP falls back to its fixed-backend mode, whose defaults accept username anonymous with any password, exposing read, write, and delete operations without the authentication the operator configured. S3 falls back to the fixed filesystem: with an authkey, any holder of that key reaches the fixed RC fs instead of the backend selected by the auth proxy.
The S3 no-authkey mode is explicitly documented as anonymous and is not part of this vulnerability claim. The confirmed S3 impact is proxy-based authorization/backend routing being ignored when S3 authentication is otherwise enabled.
Confirmed affected versions are v1.70.0 through v1.75.0, plus development commit 5629f2668c69149bf3d9d8e2a25bb32a2648606e. The dedicated CLI commands use the process-global option and are not affected by this configuration mismatch.
Weakness type: CWE-863.
Product: github.com/rclone/rclone (Go) · Assigned by: GitHub_M · Published: 2026-09-10
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Go | github.com/rclone/rclone | >= 1.70.0, < 1.75.1 | 1.75.1 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| rclone | rclone | >= 1.70.0, < 1.75.1 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 9.1 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
| GitHub | 3.1 | 9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: unchanged
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.49% probability of exploitation activity in the next 30 days; percentile 41.
Timeline
- — CVE record last updated
- — CVE record published by GitHub_M
- — GitHub-reviewed advisory GHSA-p569-5gjg-9cmj published (critical)
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-p569-5gjg-9cmj github.com
- CVE.org record CVE-2026-88044 cve.org
- NVD entry CVE-2026-88044 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com
- github.com github.com