express-rate-limit up to 8.7.1 MemoryStore race condition

Summaryinfo

A vulnerability has been found in express-rate-limit up to 8.7.1 and classified as critical. Affected by this issue is some unknown functionality of the component MemoryStore. The manipulation leads to race condition. This vulnerability is documented as CVE-2026-126204. The attack can be initiated remotely. There is not any exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in express-rate-limit up to 8.7.1. It has been rated as critical. This issue affects an unknown part of the component MemoryStore. The manipulation with an unknown input leads to a race condition vulnerability. Using CWE to declare the problem leads to CWE-362. The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently. Impacted is integrity, and availability. The summary by CVE is:

express-rate-limit is a basic rate-limiting middleware for Express. From 8.6.0 until 8.7.2, the built-in MemoryStore returns a Client whose mutable resetTime object is retained by middleware using skipFailedRequests or skipSuccessfulRequests. When a later request resets the client window, MemoryStore.resetClient mutates that same Date, so an earlier request that finishes or disconnects after the reset can pass the stale-window guard and decrement the current window's count. A client able to keep requests in flight across the boundary can obtain a bounded extra burst of up to one additional configured limit in the new window; the behavior does not increase the sustained rate. Stores that return a fresh Date are not affected. This issue is fixed in version 8.7.2.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-126204 since 11/10/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Neither technical details nor an exploit are publicly available.

Upgrading to version 8.7.2 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Name

• express-rate-limit

Version

• 8.7.0
• 8.7.1

Website

• Product: https://github.com/express-rate-limit/express-rate-limit/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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