GHSA-43fc-jf86-j433
HIGHAxios is Vulnerable to Denial of Service via __proto__ Key in mergeConfig
EPSS Exploitation Probability
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Blast Radius
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Description
Denial of Service via proto Key in mergeConfig
Summary
The mergeConfig function in axios crashes with a TypeError when processing configuration objects containing __proto__ as an own property. An attacker can trigger this by providing a malicious configuration object created via JSON.parse(), causing complete denial of service.
Details
The vulnerability exists in lib/core/mergeConfig.js at lines 98-101:
utils.forEach(Object.keys({ ...config1, ...config2 }), function computeConfigValue(prop) {
const merge = mergeMap[prop] || mergeDeepProperties;
const configValue = merge(config1[prop], config2[prop], prop);
(utils.isUndefined(configValue) && merge !== mergeDirectKeys) || (config[prop] = configValue);
});
When prop is '__proto__':
JSON.parse('{"__proto__": {...}}')creates an object with__proto__as an own enumerable propertyObject.keys()includes'__proto__'in the iterationmergeMap['__proto__']performs prototype chain lookup, returningObject.prototype(truthy object)- The expression
mergeMap[prop] || mergeDeepPropertiesevaluates toObject.prototype Object.prototype(...)throwsTypeError: merge is not a function
The mergeConfig function is called by:
Axios._request()atlib/core/Axios.js:75Axios.getUri()atlib/core/Axios.js:201- All HTTP method shortcuts (
get,post, etc.) atlib/core/Axios.js:211,224
PoC
import axios from "axios";
const maliciousConfig = JSON.parse('{"__proto__": {"x": 1}}');
await axios.get("https://httpbin.org/get", maliciousConfig);
Reproduction steps:
- Clone axios repository or
npm install axios - Create file
poc.mjswith the code above - Run:
node poc.mjs - Observe the TypeError crash
Verified output (axios 1.13.4):
TypeError: merge is not a function
at computeConfigValue (lib/core/mergeConfig.js:100:25)
at Object.forEach (lib/utils.js:280:10)
at mergeConfig (lib/core/mergeConfig.js:98:9)
Control tests performed:
| Test | Config | Result |
|---|---|---|
| Normal config | {"timeout": 5000} | SUCCESS |
| Malicious config | JSON.parse('{"__proto__": {"x": 1}}') | CRASH |
| Nested object | {"headers": {"X-Test": "value"}} | SUCCESS |
Attack scenario:
An application that accepts user input, parses it with JSON.parse(), and passes it to axios configuration will crash when receiving the payload {"__proto__": {"x": 1}}.
Impact
Denial of Service - Any application using axios that processes user-controlled JSON and passes it to axios configuration methods is vulnerable. The application will crash when processing the malicious payload.
Affected environments:
- Node.js servers using axios for HTTP requests
- Any backend that passes parsed JSON to axios configuration
This is NOT prototype pollution - the application crashes before any assignment occurs.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | axios | ≥ 1.0.0&&< 1.13.5 | 1.13.5 |
| 📦npm | axios | all versions | 0.30.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for axios. 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 axios to 1.13.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-43fc-jf86-j433 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-43fc-jf86-j433 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-43fc-jf86-j433. 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-43fc-jf86-j433 in your dependencies?
O3 detects GHSA-43fc-jf86-j433 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.