CVE
express-rate-limit rate limit bypass via MemoryStore window reset
- Exploited
- No known exploitation
- Fix
- Fixed in 8.7.2
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 8.7.2.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.27% · 20th percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 21/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
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.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity3.7/10CVSS 3.7
- No patch0/5No signal
What would change the score
- Would score about 66 if added to CISA KEV
- Would score about 61 if CISA's SSVC rates exploitation active
- Would score about 26 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 8.7.2.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
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"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- express-rate-limit express-rate-limit
From 8.6.0 · fixed in 8.7.2
Evidence 6
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-126204
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: cve.now feed data
Which versions are affected by CVE-2026-126204?
express-rate-limit: from 8.6.0 before 8.7.2.Source: cve.now feed data
How do I fix CVE-2026-126204?
Upgrade to a fixed version: 8.7.2.Source: cve.now feed data