CVE-2026-45100 OpenSIPS CVE debrief

Who should care

OpenSIPS users and administrators should be aware of this vulnerability and take steps to patch or mitigate it. They should review their deployments for exposure, update their routing configurations, and monitor their OpenSIPS instances for suspicious activity. Security teams should prioritize patching and verify that their compensating controls are effective. Operators should ensure that their platforms are protected and that they have visibility into potential exploitation attempts. Vulnerability management teams should assess their asset inventory and prioritize remediation based on risk and exposure. Security teams should also review their monitoring and detection capabilities to ensure they can identify potential exploitation attempts. Additionally, asset inventory managers should verify that their records are up-to-date and accurate. Those responsible for change management and rollback procedures should prepare for potential updates and rollbacks. Lastly, source tracking and incident response teams should be prepared to respond to potential security incidents related to this vulnerability. IT and security teams should collaborate to ensure that all necessary steps are taken to protect their environments. OpenSIPS users should also consider implementing compensating controls, such as monitoring and detection, while remediation is scheduled and verified. They should track exceptions, retest remediated assets, and close the item only after evidence is documented. Finally, they should review and update their security policies and procedures to prevent similar vulnerabilities in the future. Security teams should also consider conducting a thorough risk assessment to identify potential vulnerabilities and prioritize remediation efforts. By taking these steps, OpenSIPS users and administrators can help protect their environments from potential exploitation and minimize the risk of security incidents related to this vulnerability. OpenSIPS users should also consider reviewing their vendor patch guidance and applying patches or updates to OpenSIPS versions 3.6.6 or 4.0.0-rc1 or later. They should also review and update their routing configurations to prevent Explo-

Technical summary

The OpenSIPS server implementation has a buffer overflow vulnerability in the {s.b64encode} string transformation. The issue arises from insufficient size checks, allowing an attacker to overflow the buffer by sending a SIP message with a large header value. This can lead to remote code execution and has a CVSS score of 9.1. The vulnerability affects OpenSIPS versions 3.4.0-beta through 3.6.5 and 4.0.0-beta. Users should review their routing configurations to prevent exploitation.

Defensive priority

OpenSIPS users should prioritize patching to prevent potential remote code execution.

Recommended defensive actions

• Apply patches or updates to OpenSIPS versions 3.6.6 or 4.0.0-rc1 or later
• Review and update routing configurations to prevent exploitation
• Monitor OpenSIPS instances for suspicious activity
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record indicates a buffer overflow in OpenSIPS versions 3.4.0-beta through 3.6.5 and 4.0.0-beta. The issue is due to insufficient size checks in the {s.b64encode} string transformation, which can lead to a buffer overflow when processing large input. The CVE has a CVSS score of 9.1 and is considered CRITICAL. OpenSIPS users should verify their deployments for exposure and review routing configurations to prevent exploitation. Defenders should check for suspicious activity and monitor OpenSIPS instances.

Official resources