CVE-2019-3902 — mercurial
MEDIUMCVE-2019-3902 is a medium-severity (CVSS 5.9) Path Traversal vulnerability in mercurial. A fix is available for mercurial — see the affected versions and patch details below.
Mercurial Path Traversal/Link Following vulnerability
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2019-3902 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,987 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
mercurialReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
A flaw was found in Mercurial before 4.9. It was possible to use symlinks and subrepositories to defeat Mercurial's path-checking logic and write files outside a repository.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | mercurial | all versions | 4.9pip install --upgrade 'mercurial==4.9' |
Affected Products
debian linuxdebianmercurialmercurialenterprise linuxredhatDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mercurial, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mercurial to 4.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-3902 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
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.
Frequently Asked Questions
Is CVE-2019-3902 in your dependencies?
Find it across PyPI, including transitive dependencies.