CVE-2025-41256 identifies a cryptographic weakness in iterate GmbH's Cyberduck and Mountain Duck products, specifically related to their handling of TLS certificate pinning for untrusted certificates, such as self-signed certificates. The vulnerability arises because the certificate fingerprint used for pinning is generated using the SHA-1 hashing algorithm, which is widely recognized as cryptographically weak due to its susceptibility to collision attacks. Cyberduck versions up to 9.1.6 and Mountain Duck versions up to 4.17.5 are affected. Certificate pinning is a security mechanism designed to prevent man-in-the-middle (MITM) attacks by ensuring that the client only accepts a specific certificate or public key when establishing a TLS connection. However, by relying on SHA-1 fingerprints, an attacker with sufficient resources could potentially craft a malicious certificate that produces the same SHA-1 hash as a trusted certificate, thereby bypassing the pinning mechanism. This undermines the integrity and authenticity guarantees of TLS connections made by these applications. The CVSS v3.1 base score of 7.4 (High) reflects the network attack vector (AV:N), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), and high impact on confidentiality and integrity (C:H/I:H), with no impact on availability (A:N). There are no known exploits in the wild at the time of publication, and no patches have been linked yet. The vulnerability is categorized under CWE-328, which concerns the use of weak cryptographic primitives.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on Cyberduck and Mountain Duck for secure file transfers and cloud storage access. The weakness in certificate pinning could allow attackers to perform MITM attacks, intercepting or manipulating sensitive data in transit without detection. This threatens the confidentiality and integrity of data exchanges, potentially exposing intellectual property, personal data, or critical business information. Sectors such as finance, healthcare, legal, and government agencies, which often handle sensitive or regulated data, are particularly at risk. Additionally, organizations using self-signed certificates internally or in hybrid cloud environments are more vulnerable since the issue specifically affects untrusted certificates. The lack of required authentication or user interaction for exploitation increases the risk profile. Given the high attack complexity, exploitation may require advanced capabilities, but motivated threat actors, including cybercriminal groups or state-sponsored entities, could leverage this vulnerability to target European entities. The absence of known exploits currently reduces immediate risk but does not eliminate the potential for future attacks once exploit techniques are developed or disclosed.

European organizations should prioritize the following mitigation steps: 1) Upgrade Cyberduck and Mountain Duck to versions that replace SHA-1 with stronger hash algorithms (e.g., SHA-256) for certificate fingerprinting as soon as patches become available from iterate GmbH. 2) Until patches are released, avoid using self-signed or untrusted certificates with these applications; instead, use certificates issued by trusted Certificate Authorities (CAs) to minimize exposure. 3) Implement network-level protections such as TLS interception detection tools and anomaly-based intrusion detection systems to identify potential MITM attempts. 4) Enforce strict certificate validation policies and consider deploying certificate transparency monitoring to detect unauthorized certificate issuance. 5) Educate IT and security teams about this vulnerability to monitor for suspicious network activity involving Cyberduck or Mountain Duck. 6) Where feasible, restrict the use of these applications to controlled environments and limit exposure to untrusted networks. 7) Conduct regular security assessments and penetration tests focusing on TLS configurations and certificate pinning implementations. These targeted actions go beyond generic advice by focusing on the specific cryptographic weakness and operational contexts of the affected products.