Описание
Axios: Authentication Bypass via Prototype Pollution Gadget in validateStatus Merge Strategy
Vulnerability Disclosure: Authentication Bypass via Prototype Pollution Gadget in validateStatus Merge Strategy
Summary
The Axios library is vulnerable to a Prototype Pollution "Gadget" attack that allows any Object.prototype pollution to silently suppress all HTTP error responses (401, 403, 500, etc.), causing them to be treated as successful responses. This completely bypasses application-level authentication and error handling.
The root cause is that validateStatus is the only config property using the mergeDirectKeys merge strategy, which uses JavaScript's in operator — an operator that inherently traverses the prototype chain. When Object.prototype.validateStatus is polluted with () => true, all HTTP status codes are accepted as success.
Severity: High (CVSS 8.2)
Affected Versions: All versions (v0.x - v1.x including v1.15.0)
Vulnerable Component: lib/core/mergeConfig.js (mergeDirectKeys strategy) + lib/core/settle.js
CWE
- CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
- CWE-287: Improper Authentication
CVSS 3.1
Score: 8.2 (High)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N
| Metric | Value | Justification |
|---|---|---|
| Attack Vector | Network | PP is triggered remotely |
| Attack Complexity | Low | Once PP exists, a single property assignment exploits this. Consistent with GHSA-fvcv-3m26-pcqx |
| Privileges Required | None | No authentication needed |
| User Interaction | None | No user interaction required |
| Scope | Unchanged | Impact within the application |
| Confidentiality | Low | 401 treated as success may expose data behind auth gates |
| Integrity | High | All error handling and auth checks are silently bypassed — application operates on invalid assumptions |
| Availability | None | The function works correctly (returns true), no crash |
Usage of "Helper" Vulnerabilities
This vulnerability requires Zero Direct User Input.
If an attacker can pollute Object.prototype via any other library in the stack, Axios will automatically inherit the polluted validateStatus function during config merge. The in operator in mergeDirectKeys makes this property uniquely susceptible to prototype pollution compared to all other config properties.
Why validateStatus Is Uniquely Vulnerable
All other config properties use defaultToConfig2, which reads config2[prop] (traverses prototype). But validateStatus uses mergeDirectKeys, which uses the in operator:
The in operator is a more aggressive prototype traversal than property access. While config2['validateStatus'] also traverses the prototype, the explicit in check makes the intent clearer and the vulnerability more direct.
Proof of Concept
1. The Setup (Simulated Pollution)
2. The Gadget Trigger (Safe Code)
3. The Execution
4. The Impact
Verified PoC Output
Impact Analysis
- Authentication Bypass: Applications relying on axios rejecting 401/403 to enforce auth will silently accept unauthorized responses, allowing unauthenticated access to protected resources.
- Silent Error Swallowing: 500-series errors are treated as success, causing applications to process error bodies as valid data — leading to data corruption or logic errors.
- Security Control Bypass: Rate limiting (429), WAF blocks (403), and CAPTCHA challenges are suppressed.
- Universal Scope: Affects every axios instance in the application, including third-party libraries.
Recommended Fix
Replace the in operator with hasOwnProperty in mergeDirectKeys:
Resources
- CWE-1321: Prototype Pollution
- CWE-287: Improper Authentication
- GHSA-fvcv-3m26-pcqx: Related PP Gadget in Axios
- MDN:
inoperator - Axios GitHub Repository
Timeline
| Date | Event |
|---|---|
| 2026-04-15 | Vulnerability discovered during source code audit |
| 2026-04-15 | PoC developed and vulnerability confirmed |
| 2026-04-16 | Report revised for accuracy |
| TBD | Report submitted to vendor via GitHub Security Advisory |
Пакеты
axios
>= 1.0.0, < 1.15.1
1.15.1
axios
<= 0.31.0
0.31.1
Связанные уязвимости
Axios is a promise based HTTP client for the browser and Node.js. Prior to 1.15.1 and 0.31.1, the Axios library is vulnerable to a Prototype Pollution "Gadget" attack that allows any Object.prototype pollution to silently suppress all HTTP error responses (401, 403, 500, etc.), causing them to be treated as successful responses. This completely bypasses application-level authentication and error handling. The root cause is that validateStatus is the only config property using the mergeDirectKeys merge strategy, which uses JavaScript's in operator — an operator that inherently traverses the prototype chain. When Object.prototype.validateStatus is polluted with () => true, all HTTP status codes are accepted as success. This vulnerability is fixed in 1.15.1 and 0.31.1.
Axios is a promise based HTTP client for the browser and Node.js. Prior to 1.15.1 and 0.31.1, the Axios library is vulnerable to a Prototype Pollution "Gadget" attack that allows any Object.prototype pollution to silently suppress all HTTP error responses (401, 403, 500, etc.), causing them to be treated as successful responses. This completely bypasses application-level authentication and error handling. The root cause is that validateStatus is the only config property using the mergeDirectKeys merge strategy, which uses JavaScript's in operator — an operator that inherently traverses the prototype chain. When Object.prototype.validateStatus is polluted with () => true, all HTTP status codes are accepted as success. This vulnerability is fixed in 1.15.1 and 0.31.1.
Axios is a promise based HTTP client for the browser and Node.js. Prior to 1.15.1 and 0.31.1, the Axios library is vulnerable to a Prototype Pollution "Gadget" attack that allows any Object.prototype pollution to silently suppress all HTTP error responses (401, 403, 500, etc.), causing them to be treated as successful responses. This completely bypasses application-level authentication and error handling. The root cause is that validateStatus is the only config property using the mergeDirectKeys merge strategy, which uses JavaScript's in operator — an operator that inherently traverses the prototype chain. When Object.prototype.validateStatus is polluted with () => true, all HTTP status codes are accepted as success. This vulnerability is fixed in 1.15.1 and 0.31.1.
Axios is a promise based HTTP client for the browser and Node.js. Prio ...
