Ribbon Communications Inc.

Cybersecurity Incident Disclosure

In early September 2025, the Company became aware that unauthorized persons, reportedly associated with a nation-state actor, had gained access to the Company’s IT network. The Company promptly initiated its incident response plan and began an investigation, containment and remediation effort using multiple third-party cybersecurity experts, including federal law enforcement. While the investigation is ongoing, the Company believes that it has been successful in terminating the unauthorized access by the threat actor.

The Company has preliminarily determined that initial access by the threat actor may have occurred as early as December 2024, with final determinations dependent on completion of the ongoing investigation. As of the date of this quarterly report on Form 10-Q, we are not aware of evidence indicating that the threat actor accessed or exfiltrated any material information. Several customer files saved outside of the main network on two laptops do appear to have been accessed by the threat actor and those customers have been notified by the Company.

As of the date of this quarterly report on Form 10-Q, the Company does not believe that the incident has had a material impact, including on its financial condition or results of operations. As noted above, the Company’s investigation into this incident is ongoing and the Company continues to take additional steps to further strengthen its network security. The Company expects to incur additional costs in the fourth quarter of 2025 associated with its continued investigation into this incident, and in network strengthening efforts, however, the Company does not currently expect such costs to be material.

Insider Trading Arrangements

During the three months ended September 30, 2025, none of the Company’s directors or officers (as defined in Rule 16a-1(f) of the Securities Exchange Act of 1934)adopted, terminated or modified a Rule 10b5-1 trading arrangement ornon-Rule 10b5-1 trading arrangement (as such terms are defined in Item 408 of Regulation S-K of the Securities Act of 1933).