Listen to this Post
Introduction:
A recent bug bounty discovery revealed a critical business logic flaw where a “deleted” user retained full administrative access, including the ability to modify roles and delete other team members. This oversight highlights the risks of relying solely on frontend validation without backend enforcement—a gap that attackers can exploit to maintain persistent access.
Learning Objectives:
- Understand how incomplete user deletion can lead to privilege escalation.
- Learn backend validation techniques to enforce user revocation.
- Implement session termination best practices for deleted or deactivated accounts.
1. The Flaw: UI vs. Backend Discrepancy
Root Cause: The UI displayed user deletion, but the backend failed to revoke permissions or invalidate active sessions.
Verification Command (Linux):
Check active sessions for a "deleted" user in a typical web app (e.g., Django): psql -U postgres -c "SELECT FROM django_session WHERE session_data LIKE '%<user_id>%';"
Steps:
- Query the session table to confirm if deleted users still have active sessions.
- If sessions exist, the backend logic is flawed.
2. Mitigation: Forceful Session Termination
Solution: Invalidate sessions immediately upon user deletion.
Example (Node.js + Redis):
// Delete user and clear all sessions
app.post('/deleteUser', async (req, res) => {
await User.deleteOne({ _id: req.user.id });
// Redis command to purge sessions
redisClient.del(<code>sess:${req.sessionID}</code>, (err) => {
if (err) console.error("Session deletion failed");
});
});
Steps:
1. Ensure user deletion triggers session cleanup.
2. Use logging to verify session termination.
3. Backend Validation: Role-Based Access Control (RBAC)
Problem: The system didn’t re-check permissions post-deletion.
SQL Command to Enforce RBAC:
-- Revoke all permissions upon deletion REVOKE ALL PRIVILEGES ON ALL TABLES IN SCHEMA public FROM "<username>";
Steps:
1. Automate permission revocation in deletion workflows.
2. Audit database roles regularly.
4. Testing for Logic Flaws
Tool: OWASP ZAP or Burp Suite to replay requests after “deletion.”
Burp Suite Steps:
- Intercept a POST request to delete a user.
- Re-send the request while logged in as the “deleted” user.
- Check if the UI and backend responses conflict.
5. Cloud Hardening: AWS IAM Cleanup
AWS CLI Command:
aws iam delete-user-policies --user-name <deleted_user> aws iam delete-user --user-name <deleted_user>
Steps:
1. Automate IAM policy removal in CI/CD pipelines.
2. Use AWS Config to monitor orphaned permissions.
What Undercode Say:
- Key Takeaway 1: Frontend actions (like “Delete User”) must sync with backend state.
- Key Takeaway 2: Sessions must be invalidated globally, not just locally.
Analysis:
This flaw underscores a systemic issue in many SaaS platforms: trusting the UI to reflect backend state. Attackers can exploit such gaps to maintain “ghost access.” Future exploits may target APIs with weak deletion hooks, especially in microservices architectures where state synchronization is complex.
Prediction:
As businesses adopt more distributed systems, logic flaws like this will surge unless devops teams implement:
1. Event-driven architectures to propagate deletion events.
- Real-time permission checks at the API gateway level.
3. Automated red-team tests for session persistence scenarios.
Proactive measures today can prevent tomorrow’s breaches.
IT/Security Reporter URL:
Reported By: Joshuaingya Hello – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
