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rclone is a command-line program used to sync files and directories to and from various cloud storage providers. A critical path traversal vulnerability, known as Zip Slip, was discovered in its archive ZIP backend. This flaw affects rclone versions from 1.72.0 up to, but not including, 1.75.1. The vulnerability resides in the `(Fs).readZip` method within backend/archive/zip/zip.go. The method accepts `archive/zip.File.Name` values from an untrusted ZIP archive’s central directory without properly sanitizing them. While `path.Clean` is applied, it cannot neutralize entry names that contain more `..` components than preceding real path segments. An entry such as `”../../etc/cron.d/evil”` remains unchanged after cleaning. When an archive is mounted with an empty root (the default case), there was no verification that the resulting name stayed within the archive’s own namespace. Consequently, the malicious path was stored verbatim and returned unchanged by Object.Remote(). The `fs/sync` and `fs/operations` modules then use this `Remote()` value directly as a destination-relative path during copy or sync operations. This allows a crafted ZIP file to cause `rclone copy` or `rclone sync` to write files outside the intended destination directory on the target backend. The vulnerability is a classic example of the “Zip Slip” class of attacks. It is distinct from the `cmd/archive/extract` command, which already validates paths via its own `destPath()` function and is not affected. The issue was fixed in version 1.75.1 by skipping any ZIP entry whose cleaned and prefixed name escapes the archive’s namespace.
DailyCVE Form:
Platform: rclone
Version: 1.72.0-1.75.1
Vulnerability: Zip Slip
Severity: High
date: 2026-09-10
Prediction: 2026-09-04
What Undercode Say:
Analytics:
Inspect a malicious zip's entry names unzip -l evil.zip Expected output shows entry: ../../etc/cron.d/evil Mount the zip and list contents (vulnerable version) rclone lsf :zip:evil.zip Attempt to copy to a destination, observe path traversal rclone copy :zip:evil.zip /tmp/dest/ The file may be written outside /tmp/dest/, e.g., /etc/cron.d/evil
// Vulnerable code snippet (before fix)
for _, file := range zr.File {
remote := strings.Trim(path.Clean(file.Name), "/")
if remote == "." { remote = "" }
remote = path.Join(f.prefix, remote)
if f.root != "" {
// Ignore all files outside the root
if !strings.HasPrefix(remote, f.root) { continue }
...
}
...
o := &Object{f: f, remote: remote, ...}
dt.Add(o)
}
Exploit: (Educational Purposes!)
- Create a malicious ZIP file containing an entry with a path traversal payload, such as
"../../etc/cron.d/evil". - Host or deliver this ZIP file to a victim who uses a vulnerable rclone version.
- The victim runs a normal command like `rclone copy :zip:evil.zip dest:` or
rclone sync :zip:evil.zip dest:. - Due to the lack of path confinement, rclone will attempt to write the file outside the intended `dest` directory, potentially overwriting system files like `/etc/cron.d/evil` on the destination backend.
Protection: from this CVE
Upgrade rclone to version 1.75.1 or later. The fix ensures that any ZIP entry whose cleaned and prefixed name escapes the archive’s own namespace is skipped rather than exposed. Additionally, the pre-existing root filter’s weak prefix check was tightened to use a proper path boundary check.
Impact:
A user who runs rclone copy, sync, or `mount` against an untrusted ZIP file can have files written outside the intended destination directory on the destination backend. The actual impact depends on the confinement mechanisms of the target backend. No server compromise or custom remote configuration is required from the attacker; only a crafted ZIP file and a normal rclone invocation by the victim are needed.
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Sources:
Reported By: github.com
Extra Source Hub:
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