GHSA-4vr5-p2gc-h23p

### 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:

```go 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:

```text :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:

```text ../escaped-from-prefix.txt ```

then `path.Join("prefix", "../escaped-from-prefix.txt")` resolves to:

```text escaped-from-prefix.txt ```

As a result, the S3 backend uploads the object to:

```text bucket/safe/escaped-from-prefix.txt ```

instead of the expected destination:

```text 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

1. Extract the attached PoC ZIP.

2. Run the PoC script:

```powershell powershell -ExecutionPolicy Bypass -File .\run-poc.ps1 -RcloneExe "C:\path\to\rclone.exe" ```

3. The PoC creates a ZIP archive containing this entry:

```text ../escaped-from-prefix.txt ```

4. The PoC starts a local fake S3 endpoint and runs rclone with an S3-style destination prefix:

```powershell rclone archive extract malicious.zip :s3:bucket/safe/prefix ```

5. Observe the fake S3 request log.

Expected safe behavior:

```text PUT /bucket/safe/prefix/escaped-from-prefix.txt ```

Observed behavior:

```text 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.ps1` - `fake-s3-server.py` - `README.md` - `report-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.