CVE-2018-3721

Versions of lodash before 4.17.5 are vulnerable to prototype pollution.

The vulnerable functions are 'defaultsDeep', 'merge', and 'mergeWith' which allow a malicious user to modify the prototype of Object via __proto__ causing the addition or modification of an existing property that will exist on all objects.

CVE-2018-3721 has a CVSS score of 6.5 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.17.5); upgrading removes the vulnerable code path.

Kodem intelligence

Update to version 4.17.5 or later.

1. What is CVE-2018-3721? CVE-2018-3721 is a medium-severity security vulnerability in lodash (npm), affecting versions < 4.17.5. It is fixed in 4.17.5.
2. How severe is CVE-2018-3721? CVE-2018-3721 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2018-3721?
   • lodash (npm) (versions < 4.17.5)
   • lodash-rails (rubygems) (versions < 4.17.5)
4. Is there a fix for CVE-2018-3721? Yes. CVE-2018-3721 is fixed in 4.17.5. Upgrade to this version or later.
5. Is CVE-2018-3721 exploitable, and should I be worried? Whether CVE-2018-3721 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2018-3721 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2018-3721?
   • Upgrade lodash to 4.17.5 or later
   • Upgrade lodash-rails to 4.17.5 or later