CodeQL documentation

Unsafe code constructed from library input

ID: js/unsafe-code-construction
Kind: path-problem
Severity: warning
Precision: medium
   - security
   - external/cwe/cwe-094
   - external/cwe/cwe-079
   - external/cwe/cwe-116
Query suites:
   - javascript-security-extended.qls
   - javascript-security-and-quality.qls

Click to see the query in the CodeQL repository

When a library function dynamically constructs code in a potentially unsafe way, then it’s important to document to clients of the library that the function should only be used with trusted inputs. If the function is not documented as being potentially unsafe, then a client may incorrectly use inputs containing unsafe code fragments, and thereby leave the client vulnerable to code-injection attacks.


Properly document library functions that construct code from unsanitized inputs, or avoid constructing code in the first place.


The following example shows two methods implemented using `eval`: a simple deserialization routine and a getter method. If untrusted inputs are used with these methods, then an attacker might be able to execute arbitrary code on the system.

export function unsafeDeserialize(value) {
  return eval(`(${value})`);

export function unsafeGetter(obj, path) {
    return eval(`obj.${path}`);

To avoid this problem, either properly document that the function is potentially unsafe, or use an alternative solution such as `JSON.parse` or another library, like in the examples below, that does not allow arbitrary code to be executed.

export function safeDeserialize(value) {
  return JSON.parse(value);

const _ = require("lodash");
export function safeGetter(object, path) {
  return _.get(object, path);


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