GHSA-xp7r-j8r6-j9h3 is a high-severity (CVSS 8.2) CWE-1321 vulnerability in parse-nested-form-data. O3 Security confirms whether GHSA-xp7r-j8r6-j9h3 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
parse-nested-form-data has Prototype Pollution via `__proto__` in FormData field names
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for GHSA-xp7r-j8r6-j9h3.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-xp7r-j8r6-j9h3 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 0 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
parse-nested-form-datanpmDescription
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 [email protected]:
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]=yesa.__proto__.polluted=yes(mid-path traversal)a[0].__proto__.polluted=yes(mid-path through an array element)
constructor.prototype.x was incidentally blocked by an existing duplicate-key guard (because Object is a function and failed the JSON-object check), but relying on that was fragile, so the fix denylists constructor and prototype as well as __proto__. The array branch (a[0], a[]) was not exploitable in practice - the regex restricts array-index segments to digit characters - but the forbidden-key check is applied before the object/array type branching as defense in depth, so any future change to the regex cannot reintroduce the issue.
Impact
Any application that passes attacker-controlled FormData (or any Iterable<[string, string | File]>) to parseFormData() - typically an HTTP server processing form submissions - allows an unauthenticated remote client to mutate Object.prototype of the running process via a single field name. Concrete consequences depend on the host application and may include corrupted application state, altered control flow in code that reads ambient properties off objects, and denial of service.
Patches
Fixed in 1.0.1. handlePathPart now throws a new ForbiddenKeyError (also exported) when any path segment is __proto__, constructor, or prototype, regardless of whether the segment would be used as an object key or an array index. The check runs before object/array type branching for defense in depth.
Upgrade:
npm install parse-nested-form-data@^1.0.1
Workarounds
If upgrading is not possible, validate field names before calling parseFormData():
const FORBIDDEN = /(^|\.)(__proto__|constructor|prototype)($|[.[])/;
for (const [name] of formData.entries()) {
if (FORBIDDEN.test(name)) throw new Error('Unsafe field name');
}
Resources
- CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
- Fix commit: 527ad58eb486e32438f7198fb88315c20449d792
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | parse-nested-form-data | all versions | 1.0.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for parse-nested-form-data. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update parse-nested-form-data to 1.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-xp7r-j8r6-j9h3 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-xp7r-j8r6-j9h3 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-xp7r-j8r6-j9h3. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-xp7r-j8r6-j9h3 in your dependencies?
O3 detects GHSA-xp7r-j8r6-j9h3 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.