How severe is GHSA-8p85-9qpw-fwgw?

No CVSS score has been assigned to GHSA-8p85-9qpw-fwgw yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-8p85-9qpw-fwgw?

GHSA-8p85-9qpw-fwgw affects the following packages: @fastify/middie (npm). Ecosystems affected: npm.

How do I fix GHSA-8p85-9qpw-fwgw?

Update @fastify/middie to 9.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8p85-9qpw-fwgw is resolved across your whole dependency graph.

How do I detect GHSA-8p85-9qpw-fwgw in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @fastify/middie, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-8p85-9qpw-fwgw if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is GHSA-8p85-9qpw-fwgw actively exploited in the wild?

No public exploit code has been indexed for GHSA-8p85-9qpw-fwgw yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-8p85-9qpw-fwgw?

GHSA-8p85-9qpw-fwgw has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 37th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-8p85-9qpw-fwgw?

GHSA-8p85-9qpw-fwgw is classified as Improper Input Validation (CWE-20). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-8p85-9qpw-fwgw published, and has it been updated?

GHSA-8p85-9qpw-fwgw was published on February 28, 2026 and was last updated on February 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

@fastify/middie has Improper Path Normalization when Using Path-Scoped MiddlewareGHSA-8p85-9qpw-fwgw

Fix: fastify/middie@140e0dd

GHSA-8p85-9qpw-fwgw is a Improper Input Validation vulnerability in @fastify/middie. A fix is available for @fastify/middie — see the affected versions and patch details below.

Also known asCVE-2026-2880

Published

Feb 28, 2026

Updated

Feb 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-8p85-9qpw-fwgw.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs37th percentile — riskier than 37% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

97other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

@fastify/middienpm

2.7Mdownloads / week

Description

Summary

A path normalization inconsistency in @fastify/middie can result in authentication/authorization bypass when using path-scoped middleware (for example, app.use('/secret', auth)).

When Fastify router normalization options are enabled (such as ignoreDuplicateSlashes, useSemicolonDelimiter, and related trailing-slash behavior), crafted request paths may bypass middleware checks while still being routed to protected handlers.

Impact

An unauthenticated remote attacker can access endpoints intended to be protected by middleware-based auth/authorization controls by sending specially crafted URL paths (for example, //secret or /secret;foo=bar), depending on router option configuration.

This may lead to unauthorized access to protected functionality and data exposure.

Affected versions

Confirmed affected: @fastify/[email protected]
All versions prior to the patch are affected.

Patched versions

Fixed in: 9.2.0

Details

The issue is caused by canonicalization drift between:

@fastify/middie path matching for app.use('/prefix', ...), and
Fastify/find-my-way route lookup normalization.

Because middleware and router did not always evaluate the same normalized path, auth middleware could be skipped while route resolution still succeeded.

Workarounds

Until patched version is deployed:

Avoid relying solely on path-scoped middie guards for auth/authorization.
Enforce auth at route-level handlers/hooks after router normalization.
Disable risky normalization combinations only if operationally feasible.

Resources

Fluid Attacks Disclosure Policy: https://fluidattacks.com/advisories/policy
Fluid Attacks advisory URL: https://fluidattacks.com/advisories/jimenez

Credits

Cristian Vargas (Fluid Attacks Research Team) — discovery and report.
Oscar Uribe (Fluid Attacks) — coordination and disclosure.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@fastify/middie`	all versions	9.2.0`npm install @fastify/middie@9.2.0`

Affected Products

1 product · 1 configurations

Application

fastify\/middiefastify

< 9.2.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @fastify/middie, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @fastify/middie to 9.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8p85-9qpw-fwgw is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

## Summary A path normalization inconsistency in `@fastify/middie` can result in authentication/authorization bypass when using path-scoped middleware (for example, `app.use('/secret', auth)`). When Fastify router normalization options are enabled (such as `ignoreDuplicateSlashes`, `useSemicolonDelimiter`, and related trailing-slash behavior), crafted request paths may bypass middleware checks while still being routed to protected handlers. ## Impact An unauthenticated remote attacker can access endpoints intended to be protected by middleware-based auth/authorization controls by sending spe

O3 Security · Impact-Aware SCA

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