vulnerability / NVI-00018327 / Revision 1
parse-nested-form-data has Prototype Pollution via `__proto__` in FormData field names
GitHub lists this reviewed advisory for parse-nested-form-data. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
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8.2 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
parse-nested-form-data
source listed<= 1.0.0
## Summary `parseFormData()` walks bracket and dot-notation FormData field names into nested objects without filtering reserved property keys. A single FormData field whose name begins with `__proto__`, or contains `.__proto__.` mid-path, causes the parser to traverse onto `Object.prototype` and assign properties there, polluting the prototype chain of every plain object in the running process. ## Details The vulnerability is in `handlePathPart` in `src/index.ts`, which performs `currentObject[pathPart.path]` and `currentObject[pathPart.path] = val` for object-type path segments without rejecting reserved keys. When the segment is `__proto__`, the read returns `Object.prototype`, which then becomes the next traversal target, and the next assignment lands on the prototype. Reproduction on a fresh install of `parse-nested-form-data@1.0.0`: ```js import { parseFormData } from 'parse-nested-form-data'; const fd = new FormData(); fd.append('__proto__.polluted', 'yes'); parseFormData(fd); console.log(({}).polluted); // -> 'yes' console.log(([]).polluted); // -> 'yes' ``` Equivalent vectors: - `__proto__[polluted]=yes` - `a.__proto__.polluted=yes` (mid-path traversal) - `a[0].__pro
03 / Response
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- investigate
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04 / Limits
What this report cannot establish
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05 / Provenance
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- GHSA-xp7r-j8r6-j9h3 ↗
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- Revision 1 ·
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