GHSA-8V25-V8P6-QF7V: Path Traversal in rclone S3 API Gateway Emulation
Vulnerability ID: GHSA-8V25-V8P6-QF7V
CVSS Score: 8.6
Published: 2026-08-05
A path traversal vulnerability exists in the S3 emulation layer of rclone when executing the 'serve s3' subcommand. Because the application maps client-supplied S3 object keys containing relative directory sequences to file paths without proper boundary checks, an attacker can escape the logical containment of a target bucket. This enables unauthorized reading, writing, and deletion of files at the root level of the served storage directory.
TL;DR
The rclone 'serve s3' subcommand suffers from a path traversal vulnerability because it relies on standard Go path joining which normalizes relative sequences (..), allowing clients to access the root directory of the served storage.
⚠️ Exploit Status: POC
Technical Details
- CWE ID: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)
- Attack Vector: Network (AV:N)
- Required Privileges: None (PR:N)
- User Interaction: None (UI:N)
- CVSS v3.1 Severity Score: 8.6 (High)
- Exploit Status: PoC / Unit-Test verified
- CISA KEV Status: Not Listed
Affected Systems
- rclone S3 gateway service (rclone serve s3 subcommand) on all operational environments
-
rclone: < v1.74.4 (Fixed in:
v1.74.4)
Code Analysis
Commit: 83d1e62
Fix path traversal vulnerability in cmd/serve/s3 by enforcing canonical object key validations and rejecting relative segments.
Commit: c89b766
Cherry-pick s3 path traversal fix to release branches.
Exploit Details
- GitHub Security Advisory: Exploit methods via standard S3 client CLI utilities demonstrating boundary escape.
Mitigation Strategies
- Upgrade the rclone application to version v1.74.4 or newer immediately.
- Deploy a reverse proxy or WAF rule to block incoming request paths containing '..' or URL-encoded path traversal sequences.
- Run the rclone process under a restricted, rootless user account and restrict file system permissions to only the designated S3 directory root.
- Implement a chroot jail or container isolation to limit rclone's system visibility.
Remediation Steps:
- Check the running rclone version using command: rclone version
- If version is below v1.74.4, download the latest package from the official source or run system package managers to update.
- Apply the updated rclone executable and restart the 'serve s3' daemon process.
- If instant upgrade is unavailable, configure Nginx, HAProxy, or AWS WAF to drop requests containing pattern '..'.
References
Read the full report for GHSA-8V25-V8P6-QF7V on our website for more details including interactive diagrams and full exploit analysis.
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