CVE-2025-64340 is a medium-severity vulnerability affecting the jlowin fastmcp framework, which is widely used for building MCP applications. This vulnerability allows command injection on Windows systems when server names containing shell metacharacters (such as &) are passed to specific install commands. The issue arises from the use of subprocess.run() with a list argument, which can be exploited due to the way Windows resolves command-line arguments through cmd.exe.
The vulnerability was discovered in versions prior to 3.2.0, and has been patched in this version. The CVSS score for this vulnerability is 6.7, indicating a medium severity level, which requires attention from organizations using the affected software. Risk to organizations includes potential unauthorized command execution, leading to system compromise.
As of now, there is no public exploit available for this vulnerability, and it is not included in the Known Exploited Vulnerabilities (KEV) catalog. However, organizations should remain vigilant due to the potential risks associated with command injection vulnerabilities.
Organizations should prioritize patching immediately to mitigate this vulnerability, as it could be exploited by attackers to execute arbitrary commands on affected systems.
Vulnerability Details
The official description of this vulnerability states that it affects server names containing shell metacharacters, which may lead to command injection during the execution of install commands. This vulnerability is classified under CWE-78, indicating a command injection flaw.
The CVSS score assigned to this vulnerability is derived from its potential impact on confidentiality, integrity, and availability, which are all rated as high. The attack vector is local, meaning that an attacker must have access to the local machine to exploit this vulnerability.
This vulnerability was published on April 3, 2026, and organizations are advised to apply the patch available in version 3.2.0 to mitigate risks.
Technical Analysis
The root cause of this vulnerability is the improper handling of shell metacharacters in server names, which can be leveraged in command injection attacks. When these names are processed by cmd.exe, they can allow an attacker to execute arbitrary commands.
The attack vector is local, requiring physical or remote access to the vulnerable system. The attack complexity is considered high, as it necessitates knowledge of the command structure and the ability to influence the arguments passed to subprocess.run().
This vulnerability has low privileges required for exploitation, as users only need to execute the install commands. User interaction is required, as the attacker must provide the crafted server name.
The impacts of exploitation are significant, with high potential for confidentiality, integrity, and availability breaches, allowing attackers to manipulate the system and access sensitive information.
Risk & Impact Analysis
The real-world risk of this vulnerability is notable, especially for organizations using jlowin fastmcp in sensitive environments. The potential for command injection could lead to unauthorized access and control over affected systems.
Organizations should carefully assess their deployment of fastmcp and the environments in which it operates. The blast radius for this vulnerability can extend to any system where fastmcp is installed and configured improperly.
Given the medium severity score, organizations should address this vulnerability in their priority patch cycle, ensuring that systems are updated to version 3.2.0 or later to mitigate the risk.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The vulnerable versions of fastmcp include all versions prior to 3.2.0. Organizations should ensure that they upgrade to this version or later to mitigate the risk associated with this vulnerability.
Mitigation & Remediation
To mitigate this vulnerability, organizations should apply the patch provided in version 3.2.0 of fastmcp. If immediate patching is not possible, consider implementing workarounds such as validating server names before executing commands.
Configuration hardening measures should also be employed, including restricting the execution of commands through subprocess.run() with unvalidated inputs. Network controls can help limit access to vulnerable systems.
For a comprehensive security strategy, organizations may consider engaging in penetration testing to evaluate their security posture and identify potential vulnerabilities.
Detection Guidance
Organizations should monitor logs for indicators of attempted exploitation of this vulnerability. Look for unusual command executions and validate that server names do not contain shell metacharacters.
Behavioral anomalies in application execution patterns can also signal potential exploitation attempts. Network signatures indicating attempts to execute unauthorized commands should be established and monitored.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2025-64340 lies in its demonstration of how improper handling of user inputs can lead to severe vulnerabilities such as command injection. Security teams must remain vigilant in validating inputs.
This vulnerability represents a pattern of security oversights in software development that can expose organizations to unnecessary risks. Ongoing education and training on secure coding practices are critical.
For more insights on enhancing security measures, organizations can explore resources on penetration testing methodology and how to implement effective security protocols.
Additionally, the importance of establishing a comprehensive vulnerability management program cannot be overstated to proactively identify and address weaknesses in applications.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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