CVE-2026-57959: Hi.Events Auth Bypass Vulnerability

CVE-2026-57959 Overview

CVE-2026-57959 is a race condition vulnerability in Hi.Events through version 1.9.0. The flaw resides in the promo code validation workflow. Hi.Events validates the promo code usage count during order reservation, but the counter is only incremented later by an asynchronous UpdateEventStatisticsJob. Attackers can sequentially reserve multiple orders using the same restricted promo code. Each reservation reads order_usage_count=0 and passes validation before the increment job runs. The attacker then completes all orders at the discounted price, bypassing usage limits without needing concurrent requests. The issue is tracked under [CWE-367: Time-of-Check Time-of-Use (TOCTOU) Race Condition].

Critical Impact
Attackers can redeem limited-use promo codes an unlimited number of times, causing direct financial loss to event organizers using Hi.Events.

Affected Products

Hi.Events through version 1.9.0
Self-hosted Hi.Events deployments
Managed Hi.Events instances using the affected reservation workflow

Discovery Timeline

2026-06-29 - CVE-2026-57959 published to the National Vulnerability Database
2026-06-29 - Last updated in NVD database

Technical Details for CVE-2026-57959

Vulnerability Analysis

Hi.Events implements promo code enforcement through a two-stage workflow. The reservation stage checks the current order_usage_count value against the configured usage limit. A separate asynchronous UpdateEventStatisticsJob increments the counter after the reservation is accepted. This decoupling produces a Time-of-Check Time-of-Use (TOCTOU) window between validation and counter update. An attacker who submits reservations faster than the background job runs bypasses the usage cap. Unlike traditional race conditions, exploitation does not require concurrent requests. The attacker can submit reservations sequentially through the standard API, so exploitation is deterministic and does not depend on threading or timing precision.

Root Cause

The root cause is missing atomicity between the promo code usage check and the usage counter increment. Validation reads a stale value because the increment is deferred to an asynchronous worker. Without transactional or locking guarantees around the counter, every reservation submitted before the job completes reads the same pre-exploit value.

Attack Vector

The attack requires network access to the Hi.Events reservation endpoint and knowledge of a valid restricted promo code. The attacker issues repeated reservation calls with the same promo code before the statistics job processes any prior reservation. Each request passes validation, and the attacker then completes checkout on each reservation at the discounted price. No authentication or user interaction is required beyond standard order flow. Full technical details are available in the GitHub Issue #1223 and the VulnCheck Security Advisory.

Detection Methods for CVE-2026-57959

Indicators of Compromise

Multiple order reservations using the same restricted promo code within a short time window from a single account or IP address
Completed orders with promo code redemptions exceeding the configured max_uses limit
Reservation activity that outpaces UpdateEventStatisticsJob execution intervals in worker logs
Sudden revenue drop on events tied to a single promo code identifier

Detection Strategies

Query the database for promo codes where completed redemptions exceed the configured usage cap
Correlate reservation timestamps against UpdateEventStatisticsJob completion timestamps to identify overlap windows
Alert when the same promo code appears on more than one reservation within a short interval below the job execution period
Review web server logs for repeated POST requests to the reservation endpoint carrying identical promo code payloads

Monitoring Recommendations

Instrument the reservation endpoint with request rate metrics grouped by promo code identifier
Log every promo code validation decision with the counter value read at check time for auditability
Monitor queue depth and processing latency of UpdateEventStatisticsJob and alert on backlog growth
Track completed order counts per promo code and reconcile against expected max_uses in scheduled reports

How to Mitigate CVE-2026-57959

Immediate Actions Required

Upgrade Hi.Events beyond version 1.9.0 once a patched release is available from the maintainers
Audit historical orders for promo codes redeemed beyond their configured usage limit and reverse fraudulent redemptions
Temporarily disable restricted promo codes on high-value events until the fix is deployed
Reduce the interval between UpdateEventStatisticsJob executions to shrink the exploitation window

Patch Information

No fixed version was listed at the time of publication. Monitor the Hi.Events GitHub repository for the remediation release. The correct fix requires performing the promo code counter increment atomically inside the same database transaction as validation, or using a row-level lock on the promo code record during reservation.

Workarounds

Enforce promo code usage limits at the database layer using a unique constraint or synchronous counter update inside the reservation transaction
Apply application-level rate limiting on the reservation endpoint per user, IP address, and promo code identifier
Require authenticated accounts for redemption of restricted promo codes and cap redemptions per account
Manually reconcile promo code usage before releasing tickets or fulfilling discounted orders

bash

# Example: rate limit reservation endpoint per IP using nginx
limit_req_zone $binary_remote_addr zone=reservations:10m rate=5r/m;

location /api/orders/reserve {
    limit_req zone=reservations burst=2 nodelay;
    proxy_pass http://hievents_backend;
}