rclone archive extract allows S3 destination prefix escape via crafted archive paths

### 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.

Quoted source text, attributed separately from HOL analysis.