🔐 Proof of Concept: Meesho Android App – Insecure Cryptographic Implementation (AES-CBC without Integrity + Weak Key Derivation)

Author: Soyam Arya (aka honest_corrupt) Date of Discovery: March 2026 Affected App: Meesho Android App (com.meesho.supply) Status: Under Verification Category: Insufficient Cryptography / Data Integrity Failure

🎯 Summary

This report documents a cryptographic vulnerability in the Meesho Android application where sensitive data is encrypted using AES/CBC/PKCS5Padding without integrity protection, and the encryption key is derived using the insecure MD5 hashing algorithm.

The application constructs encrypted payloads in the format:

Base64(IV) . Base64(ciphertext)

However, due to the absence of authentication (e.g., HMAC or AEAD mode like AES-GCM), the implementation is vulnerable to:

• Ciphertext tampering
• Potential padding oracle attacks
• Weak key derivation attacks

This violates multiple OWASP Mobile Top 10 and MASVS cryptographic guidelines.

📉 Vulnerability Classification

🛠️ Technical Details

🔍 Encryption Implementation

Reverse engineering revealed the following logic:

Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

byte[] iv = new byte[16];
new SecureRandom().nextBytes(iv);

SecretKeySpec key = new SecretKeySpec(
    MD5(str), "AES"
);

cipher.init(ENCRYPT_MODE, key, new IvParameterSpec(iv));

String message = Base64(iv) + "." + Base64(ciphertext);

❌ Identified Issues

1. Weak Key Derivation (MD5)

• MD5 is deprecated and insecure
• No salt or iteration used
• Predictable key generation possible

2. Missing Integrity Protection

• No HMAC or signature applied
• Ciphertext can be modified without detection

3. Use of AES-CBC Mode

• CBC mode does not provide authenticity
• Vulnerable to padding oracle attacks if error responses differ

🎥 Proof-of-Concept (Conceptual)

The encrypted payload is transmitted in API requests as:

http POST /api/endpoint

message=Base64(IV).Base64(ciphertext)

🧪 Tampering Test

Step 1: Intercept Request

Capture request via Burp Suite:

` message=AbCdEfGhIj...xyz.KLMNOPQRST... ``

Step 2: Modify Ciphertext

Alter a single byte in ciphertext:

`` Original: ...KLMNOPQRST...

Modified: ...KLMNOPQRSU... ``

--

Step 3: Replay Request

Send modified request to server.

🔥 Observed Behavior (To be filled by tester)

• Server accepts modified ciphertext
• Response differs (possible padding oracle)
• Error message leakage
• Data manipulation observed

⚠️ Potential Impact

• Data Integrity Violation: Attackers can alter encrypted payloads
• Unauthorized Actions: Manipulation of API parameters
• Sensitive Data Exposure: Possible decryption via oracle attack
• Replay Attacks: No request authentication or nonce validation

🧪 Reproduction Steps

1. Install Meesho Android App
2. Configure Burp Suite proxy
3. Intercept API request containing message parameter
4. Modify ciphertext portion
5. Replay request and observe response

🔐 Suggested Fixes

• Replace AES-CBC with AES-GCM or ChaCha20-Poly1305
• Replace MD5 with PBKDF2 / Argon2 / bcrypt
• Implement HMAC (Encrypt-then-MAC)
• Validate integrity before decryption

🧾 Disclosure Timeline

🙋‍♂️ About the Researcher

Soyam Arya (aka honest_corrupt) CVE IDs: CVE-2025-5154, CVE-2025-6748 Mobile & Web Application Penetration Tester

• 🌐 Blog: https://soyamaryawork.blogspot.com
• 💻 GitHub: https://github.com/honestcorrupt
• 🔗 LinkedIn: https://www.linkedin.com/in/soyam-arya-a90356312