Summary
flattenizer vulnerable to prototype pollution
Overview
Prototype pollution vulnerability in ‘flattenizer’ versions 0.0.5 through 1.0.5 allows an attacker to cause a denial of service and may lead to remote code execution.
Details
The NPM module 'flattenizer' can be abused by Prototype Pollution vulnerability since the function 'unflatten()' did not check for the type of object before assigning value to the property. Due to this flaw an attacker could create a non-existent property or able to manipulate the property which leads to Denial of Service or potentially Remote code execution.
PoC Details
There is no validation before assigning the property to check whether the assigned argument is the Object's own property or not, the property polluted will be directly be assigned thereby polluting the Object prototype. Later in the code, if there is a check to validate polluted the valued would be substituted as "true" as it had been polluted.
var flattenizer = require("flattenizer")
flattenizer.unflatten({'__proto__.polluted': true});
console.log(polluted);
Impact
CVE-2020-28279 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no 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 (1.1.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2020-28279? CVE-2020-28279 is a critical-severity security vulnerability in flattenizer (npm), affecting versions >= 0.0.5, <= 1.0.5. It is fixed in 1.1.1.
- How severe is CVE-2020-28279? CVE-2020-28279 has a CVSS score of 9.8 (Critical). 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.
- Which versions of flattenizer are affected by CVE-2020-28279? flattenizer (npm) versions >= 0.0.5, <= 1.0.5 is affected.
- Is there a fix for CVE-2020-28279? Yes. CVE-2020-28279 is fixed in 1.1.1. Upgrade to this version or later.
- Is CVE-2020-28279 exploitable, and should I be worried? Whether CVE-2020-28279 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
- What actually determines whether CVE-2020-28279 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.
- How do I fix CVE-2020-28279? Upgrade
flattenizerto 1.1.1 or later.