CVE-2025-56224 identifies a security vulnerability in the One-Time Password (OTP) verification endpoint of SigningHub version 8.6.8. The core issue is the absence of rate limiting controls on the OTP verification process, which allows an attacker to perform brute force attacks by submitting numerous OTP guesses without restriction. OTP mechanisms are designed to add a second factor of authentication, enhancing security by requiring a time-sensitive code typically sent to or generated by the user. However, without rate limiting, an attacker can automate attempts to guess the correct OTP, effectively bypassing this security layer. This vulnerability compromises the integrity and confidentiality of the authentication process, potentially granting unauthorized access to sensitive documents and systems protected by SigningHub. Although no CVSS score has been assigned and no known exploits have been reported in the wild, the vulnerability's nature suggests a significant risk, especially in environments where SigningHub is used for critical digital signing workflows. The lack of patch information indicates that users must proactively implement compensating controls. The vulnerability affects all deployments of SigningHub v8.6.8 or earlier versions that do not have rate limiting on OTP verification endpoints. Attackers exploiting this flaw could gain unauthorized access, leading to data breaches, document tampering, or fraud. The vulnerability highlights the importance of implementing robust authentication controls, including rate limiting and anomaly detection, to protect against brute force attacks on OTP systems.

For European organizations, the impact of CVE-2025-56224 can be severe. SigningHub is often used in sectors requiring strong authentication for document signing, such as finance, legal, healthcare, and government. Unauthorized access through OTP bypass could lead to fraudulent document approvals, data leaks, and compromise of sensitive transactions. This undermines trust in digital signature processes and may result in regulatory non-compliance, especially under GDPR where data protection is paramount. The availability of the service might also be affected if brute force attempts cause system strain or trigger defensive lockouts. The confidentiality and integrity of signed documents are at risk, potentially causing financial losses and reputational damage. European organizations that rely heavily on SigningHub for secure workflows must consider this vulnerability a high priority to address. The absence of known exploits currently provides a window for mitigation before active exploitation occurs.

To mitigate CVE-2025-56224, organizations should immediately implement rate limiting on the OTP verification endpoint to restrict the number of attempts from a single IP address or user account within a defined time frame. This can be done via web application firewalls (WAFs), API gateways, or application-level controls. Additionally, deploying anomaly detection systems to identify unusual authentication patterns can help detect brute force attempts early. Organizations should enforce multi-factor authentication policies that do not rely solely on OTPs or combine OTPs with additional verification steps. Regularly monitoring logs for repeated failed OTP attempts and blocking offending IP addresses is recommended. If possible, update SigningHub to a patched version once available or apply vendor-provided workarounds. Educating users about phishing and social engineering risks related to OTPs can reduce the risk of credential compromise. Finally, organizations should conduct penetration testing and security assessments focusing on authentication mechanisms to ensure no similar weaknesses exist.