CVE-2026-42559 Vulnerability Analysis & Exploit Details

CVE-2026-42559
Vulnerability Scoring

8.8
/10
Severe Risk

Cybersecurity professionals consider CVE-2026-42559 an immediate threat requiring urgent mitigation.

Attack Complexity Details

  • Attack Complexity: Low
    Exploits can be performed without significant complexity or 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: Required
    User interaction is necessary for successful exploitation.

CVE-2026-42559 Details

Status: Deferred

Published on: 14 May 2026, 15:16 UTC

CVSS Release: version 3

CVSS3 Source

security-advisories@github.com

CVSS3 Type

Secondary

CVSS3 Vector

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

CVE-2026-42559 Vulnerability Summary

CVE-2026-42559: RMCP is an official Rust SDK for the Model Context Protocol. Prior to version 1.4.0, the rmcp crate's Streamable HTTP server transport (crates/rmcp/src/transport/streamable_http_server/) did not validate the incoming Host header. This allowed a malicious public website, via a DNS rebinding attack, to send authenticated requests to an MCP server running on the victim's loopback or private-network interface. This vulnerability is fixed in 1.4.0.

Assessing the Risk of CVE-2026-42559

Access Complexity Graph

The exploitability of CVE-2026-42559 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-2026-42559

With low attack complexity and no required privileges, CVE-2026-42559 is an easy target for cybercriminals. Organizations should prioritize immediate mitigation measures to prevent unauthorized access and data breaches.

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-2026-42559, 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-2026-42559, 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-2026-42559 can result in unauthorized access to sensitive data, severely compromising data privacy.
  • Integrity: High
    CVE-2026-42559 could allow unauthorized modifications to data, potentially affecting system reliability and trust.
  • Availability: High
    CVE-2026-42559 can disrupt system operations, potentially causing complete denial of service (DoS).

CVE-2026-42559 References

External References

CWE Common Weakness Enumeration

CWE-350

CAPEC Common Attack Pattern Enumeration and Classification

  • DNS Cache Poisoning CAPEC-142 A domain name server translates a domain name (such as www.example.com) into an IP address that Internet hosts use to contact Internet resources. An adversary modifies a public DNS cache to cause certain names to resolve to incorrect addresses that the adversary specifies. The result is that client applications that rely upon the targeted cache for domain name resolution will be directed not to the actual address of the specified domain name but to some other address. Adversaries can use this to herd clients to sites that install malware on the victim's computer or to masquerade as part of a Pharming attack.
  • DNS Rebinding CAPEC-275 An adversary serves content whose IP address is resolved by a DNS server that the adversary controls. After initial contact by a web browser (or similar client), the adversary changes the IP address to which its name resolves, to an address within the target organization that is not publicly accessible. This allows the web browser to examine this internal address on behalf of the adversary.
  • User-Controlled Filename CAPEC-73 An attack of this type involves an adversary inserting malicious characters (such as a XSS redirection) into a filename, directly or indirectly that is then used by the target software to generate HTML text or other potentially executable content. Many websites rely on user-generated content and dynamically build resources like files, filenames, and URL links directly from user supplied data. In this attack pattern, the attacker uploads code that can execute in the client browser and/or redirect the client browser to a site that the attacker owns. All XSS attack payload variants can be used to pass and exploit these vulnerabilities.
  • Pharming CAPEC-89 A pharming attack occurs when the victim is fooled into entering sensitive data into supposedly trusted locations, such as an online bank site or a trading platform. An attacker can impersonate these supposedly trusted sites and have the victim be directed to their site rather than the originally intended one. Pharming does not require script injection or clicking on malicious links for the attack to succeed.

Protect Your Infrastructure against CVE-2026-42559: Combat Critical CVE Threats

Stay updated with real-time CVE vulnerabilities and take action to secure your systems. Enhance your cybersecurity posture with the latest threat intelligence and mitigation techniques. Develop the skills necessary to defend against CVEs and secure critical infrastructures. Join the top cybersecurity professionals safeguarding today's infrastructures.

Other 5 Recently Published CVEs Vulnerabilities

  • CVE-2026-8293 – The Really Simple Security WordPress plugin before 9.5.10.1 does not enforce the second-factor challenge in two of its two-factor authentication R...
  • CVE-2026-8206 – The Kirki – Freeform Page Builder, Website Builder & Customizer plugin for WordPress is vulnerable to privilege escalation via account takeover in ...
  • CVE-2026-3198 – MLflow 3.9.0 with basic-auth (`--app-name basic-auth`) fails to enforce authorization checks for multiple Gateway API 'list' endpoints. Specificall...
  • CVE-2026-10583 – A security vulnerability has been detected in nextlevelbuilder GoClaw up to 3.11.3. Affected by this issue is the function Import of the file inter...
  • CVE-2026-10581 – A flaw has been found in DedeCMS 5.7.88. Affected by this vulnerability is the function base64_decode of the file /plus/download.php?open=1. This m...