fastify middie up to 9.3.1 interpretation conflict

CVSS Meta Temp Score
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CTI Interest Score
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7.3$0-$5k0.00

Summaryinfo

A vulnerability, which was classified as problematic, was found in fastify middie up to 9.3.1. This affects an unknown function. Such manipulation leads to interpretation conflict. This vulnerability is documented as CVE-2026-33804. The attack can be executed remotely. There is not any exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in fastify middie up to 9.3.1 and classified as problematic. Affected by this issue is some unknown functionality. The manipulation with an unknown input leads to a interpretation conflict vulnerability. Using CWE to declare the problem leads to CWE-436. 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. Impacted is confidentiality, integrity, and availability. CVE summarizes:

@fastify/middie versions 9.3.1 and earlier are vulnerable to middleware bypass when the deprecated Fastify ignoreDuplicateSlashes option is enabled. The middleware path matching logic does not account for duplicate slash normalization performed by Fastify's router, allowing requests with duplicate slashes to bypass middleware authentication and authorization checks. This only affects applications using the deprecated ignoreDuplicateSlashes option. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds other than disabling the ignoreDuplicateSlashes option.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-33804 since 03/23/2026. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. The technical details are unknown and an exploit is not available.

Upgrading to version 9.3.2 eliminates this vulnerability.

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Productinfo

Vendor

Name

Version

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.4
VulDB Meta Temp Score: 7.3

VulDB Base Score: 5.6
VulDB Temp Score: 5.4
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 9.1
NVD Vector: 🔒

CNA Base Score: 7.4
CNA Vector (openjs): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Interpretation conflict
CWE: CWE-436
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: middie 9.3.2

Timelineinfo

03/23/2026 CVE reserved
04/16/2026 +23 days Advisory disclosed
04/16/2026 +0 days VulDB entry created
05/17/2026 +31 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-33804 (🔒)
GCVE (CVE): GCVE-0-2026-33804
GCVE (VulDB): GCVE-100-357926

Entryinfo

Created: 04/16/2026 16:47
Updated: 05/17/2026 08:19
Changes: 04/16/2026 16:47 (62), 05/17/2026 08:19 (11)
Complete: 🔍
Cache ID: 216::103

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