CVE-2018-20990 is a high-severity (CVSS 7.5) CWE-59 vulnerability in tar. A fix is available for tar — see the affected versions and patch details below.
Arbitrary file overwrite in tar-rs
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2018-20990 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
tarReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | tar | all versions | 0.4.16cargo update -p tar --precise 0.4.16 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for tar, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update tar to 0.4.16 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-20990 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2018-20990 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2018-20990. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2018-20990 in your dependencies?
O3 Security finds CVE-2018-20990 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.