CVE-2025-69871: MedusaJS Race Condition Vulnerability

CVE-2025-69871 Overview

A race condition vulnerability exists in MedusaJS Medusa v2.12.2 and earlier in the registerUsage() function of the promotion module. The function performs a non-atomic read-check-update operation when enforcing promotion usage limits. This allows unauthenticated remote attackers to bypass usage limits by sending concurrent checkout requests, resulting in unlimited redemptions of limited-use promotional codes and potential financial loss.

Critical Impact
Unauthenticated attackers can exploit this Time-of-Check Time-of-Use (TOCTOU) vulnerability to bypass promotional code usage limits, enabling unlimited redemptions and causing significant financial damage to e-commerce businesses.

Affected Products

MedusaJS Medusa v2.12.2
MedusaJS Medusa versions prior to v2.12.2 with promotion module enabled
E-commerce platforms utilizing MedusaJS promotion functionality

Discovery Timeline

2026-02-11 - CVE CVE-2025-69871 published to NVD
2026-02-12 - Last updated in NVD database

Technical Details for CVE-2025-69871

Vulnerability Analysis

This vulnerability is classified as CWE-362 (Race Condition), specifically a Time-of-Check Time-of-Use (TOCTOU) flaw within the promotion module's usage tracking mechanism. The vulnerable registerUsage() function implements a non-atomic sequence of operations: it first reads the current usage count, checks if the limit has been reached, and then updates the counter. This design creates a critical window where concurrent requests can pass the usage check before any of them increment the counter.

The attack can be executed remotely over the network without authentication. While the attack requires precise timing coordination of concurrent requests, successful exploitation results in complete bypass of promotional code limits. This can lead to unauthorized discount redemptions, inventory manipulation, and direct financial losses for businesses operating MedusaJS-powered storefronts.

Root Cause

The root cause of this vulnerability lies in the non-atomic implementation of the promotion usage limit enforcement logic within the registerUsage() function. The function separates the read, check, and update operations instead of implementing them as a single atomic transaction. When multiple concurrent checkout requests arrive simultaneously, each request reads the same pre-incremented usage count, passes the limit validation check, and then all requests independently increment the counter. This race window allows attackers to exceed configured usage limits by the number of concurrent requests they can coordinate.

Attack Vector

The attack is executed over the network by an unauthenticated remote attacker. The attacker identifies a limited-use promotional code and then sends multiple concurrent HTTP checkout requests to the MedusaJS API endpoint, all attempting to redeem the same promotional code simultaneously. Due to the race condition in registerUsage(), each concurrent request observes the usage count before any increments are applied, allowing all requests to pass the limit check and successfully redeem the promotion. The attacker can automate this using parallel HTTP clients or multi-threaded scripts to maximize the exploitation window.

The vulnerability manifests in the promotion module's registerUsage() function where the read-check-update operation is not atomic. For detailed technical analysis and proof-of-concept information, refer to the CVE disclosure on GitHub.

Detection Methods for CVE-2025-69871

Indicators of Compromise

Promotional codes with usage counts significantly exceeding their configured limits
Multiple successful promotion redemptions from the same user or session within milliseconds
Abnormal spikes in checkout requests targeting the same promotional code endpoint
Financial discrepancies between expected and actual discount redemptions

Detection Strategies

Implement logging on promotional code usage with timestamps to identify concurrent redemption patterns
Monitor for high-frequency API requests to checkout endpoints with identical promotional codes
Set up alerts for promotional code usage exceeding configured limits
Analyze request timing patterns to detect coordinated concurrent exploitation attempts

Monitoring Recommendations

Enable detailed audit logging on the MedusaJS promotion module to track all redemption attempts
Implement rate limiting on checkout endpoints to reduce the effectiveness of concurrent exploitation
Configure real-time monitoring dashboards for promotional code usage metrics
Review financial reconciliation reports regularly to detect unauthorized discounts

How to Mitigate CVE-2025-69871

Immediate Actions Required

Upgrade MedusaJS Medusa to a patched version that addresses the race condition in registerUsage()
Review and audit all promotional code usage records for evidence of exploitation
Temporarily disable high-value promotional codes until the patch is applied
Implement server-side rate limiting on checkout API endpoints as a defense-in-depth measure

Patch Information

A fix for this vulnerability has been submitted via Pull Request #13760 on the official MedusaJS GitHub repository. Organizations should monitor the MedusaJS repository for official releases incorporating this fix and upgrade to the patched version as soon as it becomes available.

Workarounds

Implement database-level locking or atomic increment operations on the promotion usage counter at the application layer
Add rate limiting middleware to restrict concurrent requests from the same source to checkout endpoints
Use pessimistic locking in the database layer to serialize access to promotion usage records during checkout
Consider temporarily disabling the promotion module functionality until the official patch is applied

bash

# Example: Implement rate limiting on checkout endpoints using nginx
# Add to nginx configuration for MedusaJS proxy

# Define rate limiting zone for checkout endpoints
limit_req_zone $binary_remote_addr zone=checkout_limit:10m rate=5r/s;

# Apply rate limiting to checkout API routes
location /store/carts {
    limit_req zone=checkout_limit burst=10 nodelay;
    proxy_pass http://medusa_backend;
}