CVE-2025-54320 identifies a vulnerability in Ascertia SigningHub, a digital signature management platform, specifically in versions up to 8.6.8. The issue arises from the absence of rate limiting controls on the 'invite user' functionality. An authenticated attacker can exploit this by programmatically sending a large number of invite requests to one or multiple email addresses. This results in an email bombing attack, where the victim's inbox is flooded with invitation emails, potentially overwhelming email servers or causing denial of service to legitimate users. The vulnerability requires the attacker to have valid credentials, which limits exploitation to insiders or compromised accounts. There is no evidence of public exploits in the wild, and no patch or CVSS score is currently available. The lack of rate limiting is a design flaw that could be mitigated by implementing thresholds on invite request frequency per user or IP address. The attack does not directly compromise confidentiality or integrity but impacts availability and user experience. Organizations using SigningHub for critical digital signing workflows may experience operational disruptions and increased support costs due to this vulnerability.

For European organizations, the primary impact is operational disruption caused by email bombing, which can degrade email system availability and overwhelm users with unsolicited invites. This can lead to decreased productivity, increased helpdesk workload, and potential reputational damage if customers or partners are affected. Organizations relying heavily on Ascertia SigningHub for legally binding digital signatures may face delays in document processing and compliance risks if users are unable to receive or respond to invites promptly. Although the vulnerability requires authentication, insider threats or compromised accounts increase risk. The attack does not directly expose sensitive data but can be leveraged as a nuisance or denial-of-service vector. In sectors such as finance, legal, and government where digital signatures are critical, the impact could be more pronounced. The lack of public exploits suggests limited immediate risk, but proactive mitigation is essential to prevent escalation.

To mitigate CVE-2025-54320, organizations should implement strict rate limiting on the invite user function within SigningHub, either through configuration if supported or via network/application layer controls such as web application firewalls. Monitoring and alerting on unusual invite request patterns can help detect abuse early. Enforce strong authentication and session management to reduce the risk of compromised accounts being used for exploitation. Organizations should engage with Ascertia to obtain patches or updates addressing this vulnerability and apply them promptly once available. Additionally, educating users about suspicious invite emails and providing mechanisms to report abuse can reduce impact. If possible, temporarily disabling the invite function or restricting it to trusted administrators until a fix is applied can limit exposure. Email filtering solutions should be tuned to handle potential invite floods to protect end users. Finally, reviewing and tightening access controls around SigningHub accounts will reduce the attack surface.