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CVE-2025-41256: Weak TLS Certificate Pinning in Cyberduck and Mountain Duck

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Overview

The vulnerability CVE-2025-41256 highlights an improper handling of TLS certificate pinning in Cyberduck and Mountain Duck. The affected software fails to properly pin untrusted certificates, particularly self-signed ones, due to the usage of the SHA-1 hashing algorithm, which is known to be weak. This vulnerability could potentially lead to system compromise or data leakage, posing a significant risk to users and organizations who rely on these software for their operations.

Vulnerability Summary

CVE ID: CVE-2025-41256
Severity: High (7.4/10)
Attack Vector: Network
Privileges Required: None
User Interaction: Required
Impact: Potential system compromise or data leakage

Affected Products

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Product | Affected Versions

Cyberduck | up to 9.1.6
Mountain Duck | up to 4.17.5

How the Exploit Works

The exploiter can take advantage of this vulnerability by posing as a legitimate entity and presenting a self-signed certificate. Since the software improperly pins this untrusted certificate and stores the certificate fingerprint as weak SHA-1, it becomes susceptible to a ‘man-in-the-middle’ (MitM) attack. By intercepting and altering communications between two parties, an attacker could potentially compromise the system or leak sensitive data.

Conceptual Example Code

Below is a conceptual example of how this vulnerability might be exploited. In this case, the attacker presents a self-signed certificate during the TLS handshake.

POST /tls-handshake HTTP/1.1
Host: target.example.com
Content-Type: application/tls-certificate
{ "certificate": "self-signed-certificate", "fingerprint": "SHA-1-fingerprint" }

Upon receiving this request, the vulnerable software would improperly pin the untrusted self-signed certificate, opening up the possibility for a ‘man-in-the-middle’ attack.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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