CVE-2026-116789: FreeSWITCH: DTLS-SRTP peer certificate is not bound to the SDP fingerprint when FreeSWITCH is the DTLS server
FreeSWITCH is a Software Defined Telecom Stack enabling the digital transformation from proprietary telecom switches to a software implementation that runs on any commodity hardware. Prior to 1.11.2, dtlsstatesetup() compared a peer certificate with the SDP a=fingerprint only when FreeSWITCH was the DTLS client, not when it held the DTLS server role. An unauthenticated peer able to reach the negotiated media port could complete the DTLS-SRTP handshake with an unrelated certificate, obtain the leg's SRTP keys, decrypt and inject media, and displace the legitimate endpoint; on ICE-enabled legs the peer also needs the connectivity-check credentials from SDP, which generally requires signaling visibility or a position on its path. WebRTC and SIP DTLS-SRTP legs are affected whenever the peer selects the active role, while FreeSWITCH client-role handshakes already perform fingerprint validation. Version 1.11.2 introduces the remediation, which requires rtpdtlsclientcertverifymode=fingerprint.
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
FreeSWITCHto a version that resolves this vulnerability.Fixed in 1.11.2 - Configuration
Set rtp_dtls_client_cert_verify_mode to fingerprint.
FreeSWITCH rtp_dtls_client_cert_verify_mode = fingerprint
Event History
Frequently Asked Questions
Which deployments are exposed?
WebRTC and SIP DTLS-SRTP legs are affected when the peer selects the active DTLS role, causing FreeSWITCH to act as the DTLS server. FreeSWITCH handshakes in the DTLS client role already validate the SDP fingerprint.
What does an attacker need to exploit this?
An unauthenticated attacker must be able to reach the negotiated media port and complete a DTLS-SRTP handshake using an unrelated certificate. On ICE-enabled legs, the attacker also needs the SDP connectivity-check credentials, which generally requires signaling visibility or being on the signaling path.
What could a successful attacker do?
The attacker can obtain the call leg's SRTP keys, decrypt and inject media, and displace the legitimate endpoint.
What configuration is required after upgrading?
The remediation introduced in version 1.11.2 requires setting rtp_dtls_client_cert_verify_mode=fingerprint.