CVE-2026-33804 Vulnerability Analysis & Exploit Details

CVE-2026-33804
Vulnerability Scoring

7.4
/10
Very High Risk

Highly exploitable, CVE-2026-33804 poses a critical security risk that could lead to severe breaches.

Attack Complexity Details

  • Attack Complexity: High
    Exploits require significant effort and special conditions.
  • Attack Vector: Network
    Vulnerability is exploitable over a network without physical access.
  • Privileges Required: None
    No privileges are required for exploitation.
  • Scope: Unchanged
    Exploit remains within the originally vulnerable component.
  • User Interaction: None
    No user interaction is necessary for exploitation.

CVE-2026-33804 Details

Status: Received on 16 Apr 2026, 15:17 UTC

Published on: 16 Apr 2026, 15:17 UTC

CVSS Release: version 3

CVSS3 Source

ce714d77-add3-4f53-aff5-83d477b104bb

CVSS3 Type

Secondary

CVSS3 Vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CVE-2026-33804 Vulnerability Summary

CVE-2026-33804: @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.

Assessing the Risk of CVE-2026-33804

Access Complexity Graph

The exploitability of CVE-2026-33804 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).

Exploitability Analysis for CVE-2026-33804

CVE-2026-33804 presents a challenge to exploit due to its high attack complexity, but the absence of privilege requirements still makes it a viable target for skilled attackers. A thorough security review is advised.

Understanding AC and PR

A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.

Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.

Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.

CVSS Score Breakdown Chart

Above is the CVSS Sub-score Breakdown for CVE-2026-33804, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.

CIA Impact Analysis

Below is the Impact Analysis for CVE-2026-33804, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.

  • Confidentiality: High
    Exploiting CVE-2026-33804 can result in unauthorized access to sensitive data, severely compromising data privacy.
  • Integrity: High
    CVE-2026-33804 could allow unauthorized modifications to data, potentially affecting system reliability and trust.
  • Availability: None
    CVE-2026-33804 does not impact system availability.

CVE-2026-33804 References

External References

CWE Common Weakness Enumeration

CWE-436

CAPEC Common Attack Pattern Enumeration and Classification

  • HTTP Request Splitting CAPEC-105 An adversary abuses the flexibility and discrepancies in the parsing and interpretation of HTTP Request messages by different intermediary HTTP agents (e.g., load balancer, reverse proxy, web caching proxies, application firewalls, etc.) to split a single HTTP request into multiple unauthorized and malicious HTTP requests to a back-end HTTP agent (e.g., web server). See CanPrecede relationships for possible consequences.
  • HTTP Response Smuggling CAPEC-273 An adversary manipulates and injects malicious content in the form of secret unauthorized HTTP responses, into a single HTTP response from a vulnerable or compromised back-end HTTP agent (e.g., server). See CanPrecede relationships for possible consequences. Modification/manipulation of HTTP message headers, request-line and body parameters to disrupt and interfere in the interpretation and parsing of HTTP message lengths/boundaries for consecutive HTTP messages by HTTP agents in a HTTP chain or network path.
  • HTTP Response Splitting CAPEC-34 An adversary manipulates and injects malicious content, in the form of secret unauthorized HTTP responses, into a single HTTP response from a vulnerable or compromised back-end HTTP agent (e.g., web server) or into an already spoofed HTTP response from an adversary controlled domain/site. See CanPrecede relationships for possible consequences.

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