GHSA-j5gw-2vrg-8fgx astral-tokio-tar Vulnerable to PAX Header Desynchronization

• crates.io astral-tokio-tar: < 0.5.6 → fixed in 0.5.6 • crates.io tokio-tar: <= 0.3.1 (no fix yet)

Summary Versions of `astral-tokio-tar` prior to 0.5.6 contain a boundary parsing vulnerability that allows attackers to smuggle additional archive entries by exploiting inconsistent PAX/ustar header handling. When processing archives with PAX-extended headers containing size overrides, the parser incorrectly advances stream position based on ustar header size (often zero) instead of the PAX-specified size, causing it to interpret file content as legitimate tar headers. This vulnerability was disclosed to multiple Rust tar parsers, all derived from the original `async-tar` fork of `tar-rs`. Details Vulnerability Description The vulnerability stems from inconsistent handling of PAX extended headers versus ustar headers when determining file data boundaries. Specifically: 1. PAX header correctly specifies the file size (e.g., `size=1048576`) 2. ustar header incorrectly specifies zero size (`size=000000000000`) 3. tokio-tar advances the stream position based on the ustar size (0 bytes) 4. Inner content is then interpreted as legitimate outer archive entries Attack Mechanism When a TAR file contains: • An outer entry with PAX `size=N` but ustar `size=0` • File data that begins with valid TAR header structures • The parser treats inner content as additional outer entries This creates a header/data desynchronization where the parser's position becomes misaligned with actual file boundaries. Root Cause ```rust // Vulnerable: Uses ustar size instead of PAX override let file_size = header.size(); // Returns 0 from ustar field let next_pos = current_pos + 512 + pad_to_512(file_size); // Advances 0 bytes // Fixed: Apply PAX overrides before position calculation let mut file_size = header.size(); if let Some(pax_size) = pending_pax.get("size") { file_size = pax_size.parse().unwrap(); } let next_pos = current_pos + 512 + pad_to_512(file_size); // Correct advance ``` Impact The impact of this vulnerability depends on where `astral-tokio-tar` is used, and whether it is used to extract untrusted tar archives. If used to extract untrusted inputs, it may result in unexpected attacker-controlled access to the filesystem, in turn potential resulting in arbitrary code execution or credential exfiltration. See GHSA-w476-p2h3-79g9 for how this vulnerability affects `uv`, `astral-tokio-tar`'s primary downstream user. Observe that unlike this advisory,` uv`'s advisory is considered low severity due to overlap with intentional existing capabilities in source distributions. Workarounds Users are advised to upgrade to version 0.5.6 or newer to address this advisory. There is no workaround other than upgrading. Timeline | Date | Event | | --- | --- | | Aug 21, 2025 | Vulnerability discovered by Edera Security Team | | Aug 21, 2025 | Initial analysis and PoC confirmed | | Aug 22, 2025 | Maintainers notified (privately) | | Aug 25, 2025 | Private patch and test suite shared | | Oct 7, 2025 | Text freeze for GHSA | | Oct 21, 2025 | Coordinated public disclosure and patched releases | Credits • Discovered by: Steven Noonan (Edera) and Alex Zenla (Edera) • Coordinated disclosure: Ann Wallace (Edera)