#VU58206 Absolute Path Traversal in tar - CVE-2021-32803

Vulnerability identifier: #VU58206

Vulnerability risk: Medium

CVSSv4.0: 6.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2021-32803

CWE-ID: CWE-36

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
tar
Web applications / JS libraries

Vendor: npm Inc.

Description

The vulnerability allows a remote attacker to overwrite arbitrary files on the system.

The vulnerability exists due to a logic issue when extracting tar files that contained both a directory and a symlink with the same name as the directory. This order of operations resulted in the directory being created and added to the node-tar directory cache. When a directory is present in the directory cache, subsequent calls to mkdir for that directory are skipped. However, this is also where node-tar checks for symlinks occur.

By first creating a directory, and then replacing that directory with a symlink, it was thus possible to bypass node-tar symlink checks on directories, essentially allowing an untrusted tar file to symlink into an arbitrary location and subsequently extracting arbitrary files into that location, thus allowing arbitrary file creation and overwrite.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

tar: 3.0.0 - 6.1.1

---

External links
https://github.com/npm/node-tar/security/advisories/GHSA-r628-mhmh-qjhw
https://github.com/npm/node-tar/commit/9dbdeb6df8e9dbd96fa9e84341b9d74734be6c20

---

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.