CVE-2021-33838 – The Luca COVID-19 contact tracing app for Andro... (How to Fix)

📋 TL;DR

The Luca COVID-19 contact tracing app for Android versions through 1.7.4 leaks sensitive information about users' COVID-19 status. Remote attackers can correlate check-in state requests with phone number registration requests to determine whether users have been flagged for COVID-19 exposure. This affects all users of the vulnerable Luca app versions.

💻 Affected Systems

Products:

Luca COVID-19 contact tracing app

Versions: through 1.7.4

Operating Systems: Android

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects the Android version of the Luca app. iOS version may have different security characteristics.

📦 What is this software?

Luca by Luca App

View all CVEs affecting Luca →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Attackers could identify specific individuals who have tested positive for COVID-19, enabling targeted harassment, discrimination, or social engineering attacks based on health status.

🟠

Likely Case

Attackers monitoring network traffic could statistically identify groups of users who have been exposed to COVID-19, potentially revealing outbreak patterns or compromising privacy of affected individuals.

🟢

If Mitigated

With proper network segmentation and encryption, the correlation attack becomes significantly more difficult, though not impossible for determined attackers with network access.

🌐 Internet-Facing: MEDIUM - The app communicates with backend servers over the internet, but exploitation requires intercepting or monitoring specific API calls and correlating timing patterns.

🏢 Internal Only: LOW - This is primarily a mobile app vulnerability affecting individual users rather than internal enterprise systems.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires network monitoring capabilities and timing analysis of API requests. The vulnerability is well-documented with public technical analysis.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Versions after 1.7.4

Vendor Advisory: https://luca-app.de/securityoverview/properties/objectives.html

Restart Required: Yes

Instructions:

1. Open Google Play Store on Android device
2. Search for 'Luca'
3. If update available, tap 'Update'
4. Restart the app after update completes

🔧 Temporary Workarounds

Disable app or use alternative

android

Uninstall the vulnerable Luca app version or use an alternative COVID-19 contact tracing solution

adb uninstall de.culture4life.luca

Use VPN for all app traffic

android

Route all Luca app traffic through a trusted VPN to prevent network monitoring

🧯 If You Can't Patch

Disable the Luca app completely until patched
Use device-level VPN to encrypt all network traffic from the device

🔍 How to Verify

Check if Vulnerable:

Check app version in Android Settings > Apps > Luca > App info. If version is 1.7.4 or earlier, you are vulnerable.

Check Version:

adb shell dumpsys package de.culture4life.luca | grep versionName

Verify Fix Applied:

Verify app version is greater than 1.7.4 in app settings. Monitor network traffic to confirm timing correlation between check-in and registration requests is no longer detectable.

📡 Detection & Monitoring

Log Indicators:

Multiple API calls to Luca backend with trace IDs in quick succession
Pattern of check-in state requests followed by phone registration requests within short time windows

Network Indicators:

HTTP/HTTPS traffic to Luca backend servers with specific API endpoints being called in predictable sequences
Correlation of timing between /checkin and /register API calls

SIEM Query:

source="network_traffic" dest_ip="luca-backend-ips" (uri_path="/api/checkin" OR uri_path="/api/register") | stats count by src_ip, uri_path | where count > threshold

📊 Metadata

CVE ID: CVE-2021-33838

CVSS v3 Score: 7.5 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CWE: CWE-203

Published: June 4, 2021

Last Updated: November 21, 2024

🔗 References

https://github.com/mame82/misc/blob/master/luca_traceIds.md Third Party Advisory
https://luca-app.de/securityoverview/properties/objectives.html Vendor Advisory
https://www.ccc.de/de/updates/2021/luca-app-ccc-fordert-bundesnotbremse Third Party Advisory
https://www.youtube.com/playlist?list=PLKuX6iczGb3kuDsm2RFgbmRkTugkR9-UE Exploit,Third Party Advisory
https://github.com/mame82/misc/blob/master/luca_traceIds.md Third Party Advisory
https://luca-app.de/securityoverview/properties/objectives.html Vendor Advisory
https://www.ccc.de/de/updates/2021/luca-app-ccc-fordert-bundesnotbremse Third Party Advisory
https://www.youtube.com/playlist?list=PLKuX6iczGb3kuDsm2RFgbmRkTugkR9-UE Exploit,Third Party Advisory

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