Miggo at BlackHat 2026!
Easily map the attack path and prioritize which CVEs are a threat to your organization
Miggo AIGenerate vendor-ready rules for the observed attack patterns, plus reasoning and safe deployment guidance
| Package Name | Ecosystem | Vulnerable Versions | First Patched Version |
|---|---|---|---|
| express | npm | < 4.22.0 | 4.22.0 |
| express | npm | >= 5.0.0, < 5.1.0 | 5.1.0 |
Miggo AIRoot Cause AnalysisThe vulnerability lies in the express framework's extended query parser, which is the default in version 4. The parseExtendedQueryString function in lib/utils.js used the qs.parse library with the allowPrototypes: true option. This configuration allows the query string to contain parameters that can modify properties of the global Object.prototype. An attacker could craft a malicious query string like ?hasOwnProperty=foo to overwrite built-in Object methods, potentially leading to application crashes or other unpredictable behavior when other parts of the code rely on these prototype properties. The provided patch addresses this by replacing allowPrototypes: true with plainObjects: true, which instructs qs.parse to create a plain object with a null prototype, effectively isolating the parsed query parameters and preventing prototype pollution.
