CVE-2019-15608 is a medium-severity (CVSS 5.9) CWE-840 vulnerability in yarn. 1 public exploit reference exists, so weaponization risk is real. A fix is available for yarn — see the affected versions and patch details below.
TOCTOU Race Condition in Yarn
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2019-15608 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
yarnnpmDescription
The package integrity validation in yarn < 1.19.0 contains a TOCTOU vulnerability where the hash is computed before writing a package to cache. It's not computed again when reading from the cache. This may lead to a cache pollution attack. This issue is fixed in 1.19.0.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | yarn | all versions | 1.19.0npm install yarn@1.19.0 |
Affected Products
yarnyarnpkgResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for yarn, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update yarn to 1.19.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-15608 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.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Run 'yarn cache clean' before installs.Source: Red Hat security advisory for CVE-2019-15608 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2019-15608 in your dependencies?
Find it across npm, including transitive dependencies.