@fastify/middie vulnerable to path-scoped middleware bypass via absolute-form request target (CVE-2026-85184)
Published Last modified Sources: CVE.org
What is affected, what to do
@fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching against the raw request target, while the Fastify router resolves an absolute-form request target to its path before dispatching. Because the two layers evaluate different strings, a request using an absolute-form target reaches the route handler while the path-scoped middleware, such as authentication or authorization, is skipped.
Update @fastify/middie to version 9.3.4.
- Affected
- @fastify/middie
lt 9.1.0..9.3.4
- @fastify/middie
- Fixed in
- @fastify/middie
9.3.4
- @fastify/middie
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Metrics
9.1
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v3
9.1
CVSS v3
Severity Critical on the scale from 0 to 10.
Source: CVE.org
0.5 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 44.2
Show all metrics
- Severity
- Critical
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 86.82 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 9.1 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 9.1
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 0.5 %
- Low — model estimates < 1% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 44.2
- High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-436
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
@fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching against the raw request target, while the Fastify router resolves an absolute-form request target to its path before dispatching. Because the two layers evaluate different strings, a request using an absolute-form target reaches the route handler while the path-scoped middleware, such as authentication or authorization, is skipped. An unauthenticated network attacker can use this to bypass path-based access controls in a Fastify application that relies on middie for those controls. Users should upgrade to @fastify/middie 9.3.4 or later.
Source: NVD (NIST), cvelistv5
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| @fastify/middie | @fastify/middie |
|
|
| fastify | fastify\/middie |
|
|
Vendors and products
Weakness classes (CWE)
CWE-436Interpretation Conflict
Class
Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.
Entry at MITRE CWE-436
References & sources
- github.comfastify/middie/security/advisories/GHSA-hx87-8wv7-pjv8
- cna.openjsf.orgsecurity-advisories.html
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Initial analysis by NVDNVD
Newly listed as affected:- HackerOne fastify/middie (9.1.0 – before 9.3.4)
Show 3 original changes
Individual changes of this event as published by NVD Type Action Before After Product configuration added —OR *cpe:2.3:a:fastify:fastify/middie:*:*:*:*:*:node.js:*:* versions from (including) 9.1.0 up to (excluding) 9.3.4Reference type added —openjs: https://cna.openjsf.org/security-advisories.html Types: Third Party AdvisoryReference type added —openjs: https://github.com/fastify/middie/security/advisories/GHSA-hx87-8wv7-pjv8 Types: Mitigation, Vendor AdvisorySource identifier: nvd@nist.gov
Record modifiedCISA ADP
CISA assessment (SSVC): exploitation: none known, automatable: yes
Show the original change
Individual changes of this event as published by NVD Type Action Before After SSVC assessment added —{"id":"CVE-2026-85184","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-09-04T19:36:12.098740Z"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
ReceivedOpenJS Foundation
CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Weakness type: CWE-436
Description added or changed
Show 6 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —@fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching against the raw request target, while the Fastify router resolves an absolute-form request target to its path before dispatching. Because the two layers evaluate different strings, a request using an absolute-form target reaches the route handler while the path-scoped middleware, such as authentication or authorization, is skipped. An unauthenticated network attacker can use this to bypass path-based access controls in a Fastify application that relies on middie for those controls. Users should upgrade to @fastify/middie 9.3.4 or later.CVSS added —AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:NWeakness type (CWE) added —CWE-436Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/85xxx/CVE-2026-85184.json">CVE-2026-85184</a>Reference added —https://cna.openjsf.org/security-advisories.htmlReference added —https://github.com/fastify/middie/security/advisories/GHSA-hx87-8wv7-pjv8Source identifier: ce714d77-add3-4f53-aff5-83d477b104bb
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-85184"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-85184.svg?lang=en" alt="CVE-2026-85184 – NEOSEC Intel" height="20"></a>