Summary
rclone archive extract can write extracted files outside the user-selected destination prefix when extracting a crafted archive. A malicious archive entry containing parent path components such as ../ can escape the requested extraction prefix and create or overwrite sibling objects in the same bucket/path scope.
Details
The affected code path is in cmd/archive/extract/extract.go.
In ArchiveExtract(), the archive entry path is taken from f.NameInArchive. The code strips only a leading ./ prefix and then joins the archive entry path with the destination directory:
remote := f.NameInArchive
remote = strings.TrimPrefix(remote, "./")
if dstDir != "" {
remote = path.Join(dstDir, remote)
}
_, err = operations.Rcat(ctx, dst, remote, fin, f.ModTime(), nil)Parent path components such as ../ are not rejected before path.Join() is used.
When the destination is an S3-style remote such as:
:s3:bucket/safe/prefix
rclone creates the destination filesystem rooted at bucket/safe and treats prefix as the destination directory. If the archive contains an entry named:
../escaped-from-prefix.txt
then path.Join("prefix", "../escaped-from-prefix.txt") resolves to:
escaped-from-prefix.txt
As a result, the S3 backend uploads the object to:
bucket/safe/escaped-from-prefix.txt
instead of the expected destination:
bucket/safe/prefix/escaped-from-prefix.txt
This allows an attacker-controlled archive to escape the selected extraction prefix on object-storage remotes.
PoC
Test environment:
- Windows 11
- rclone v1.74.3 official Windows amd64 binary
- Local fake S3 HTTP endpoint
- Crafted ZIP archive containing
../escaped-from-prefix.txt
Steps to reproduce:https://drive.google.com/file/d/1P_cLKFgiWSVSATB8500yP28jdzwt9FAt/view?usp=sharing
-
Extract the attached PoC ZIP.
-
Run the PoC script:
powershell -ExecutionPolicy Bypass -File .\run-poc.ps1 -RcloneExe "C:\path\to\rclone.exe"
- The PoC creates a ZIP archive containing this entry:
../escaped-from-prefix.txt
- The PoC starts a local fake S3 endpoint and runs rclone with an S3-style destination prefix:
rclone archive extract malicious.zip :s3:bucket/safe/prefix
- Observe the fake S3 request log.
Expected safe behavior:
PUT /bucket/safe/prefix/escaped-from-prefix.txt
Observed behavior:
PUT /bucket/safe/escaped-from-prefix.txt?x-id=PutObject
This shows that the archive entry escaped the requested safe/prefix destination and was written under safe/ instead.
The PoC package includes:
run-poc.ps1fake-s3-server.pyREADME.mdreport-draft.md- captured proof logs
Impact
An attacker who supplies an archive that a victim extracts with rclone archive extract can cause extracted files to be written outside the destination prefix selected by the victim when the destination is an S3-style object storage remote.
Depending on the victim's configured remote credentials and bucket permissions, this may allow creation or overwrite of sibling objects outside the intended extraction directory/prefix.
This does not require compromising the S3 service itself. The attack relies on the victim extracting an attacker-controlled archive with rclone into an object-storage prefix.
References
Summary
rclone archive extractcan write extracted files outside the user-selected destination prefix when extracting a crafted archive. A malicious archive entry containing parent path components such as../can escape the requested extraction prefix and create or overwrite sibling objects in the same bucket/path scope.Details
The affected code path is in
cmd/archive/extract/extract.go.In
ArchiveExtract(), the archive entry path is taken fromf.NameInArchive. The code strips only a leading./prefix and then joins the archive entry path with the destination directory:Parent path components such as
../are not rejected beforepath.Join()is used.When the destination is an S3-style remote such as:
rclone creates the destination filesystem rooted at
bucket/safeand treatsprefixas the destination directory. If the archive contains an entry named:then
path.Join("prefix", "../escaped-from-prefix.txt")resolves to:As a result, the S3 backend uploads the object to:
instead of the expected destination:
This allows an attacker-controlled archive to escape the selected extraction prefix on object-storage remotes.
PoC
Test environment:
../escaped-from-prefix.txtSteps to reproduce:https://drive.google.com/file/d/1P_cLKFgiWSVSATB8500yP28jdzwt9FAt/view?usp=sharing
Extract the attached PoC ZIP.
Run the PoC script:
Expected safe behavior:
Observed behavior:
This shows that the archive entry escaped the requested
safe/prefixdestination and was written undersafe/instead.The PoC package includes:
run-poc.ps1fake-s3-server.pyREADME.mdreport-draft.mdImpact
An attacker who supplies an archive that a victim extracts with
rclone archive extractcan cause extracted files to be written outside the destination prefix selected by the victim when the destination is an S3-style object storage remote.Depending on the victim's configured remote credentials and bucket permissions, this may allow creation or overwrite of sibling objects outside the intended extraction directory/prefix.
This does not require compromising the S3 service itself. The attack relies on the victim extracting an attacker-controlled archive with rclone into an object-storage prefix.
References