PatchSiren cyber security CVE debrief

CVE-2026-45103 OpenSIPS CVE debrief

OpenSIPS, a Session Initiation Protocol (SIP) server implementation, has a vulnerability in versions prior to 3.6.6 and 4.0.0-rc1. The TCP message framing layer improperly parses the Content-Length header using unsigned int arithmetic with no overflow check. An attacker can send a Content-Length value that overflows unsigned int (e.g., 4294967296), causing the framing layer to compute a wrapped-around value (e.g., 0) and split the TCP stream at the wrong boundary. This enables SIP message smuggling, allowing unauthenticated, network-based attackers to smuggle arbitrary SIP messages over TCP-based transports (proto_tcp, proto_tls, proto_ws, proto_wss). The vulnerability allows smuggled messages to bypass front-end SBC/proxy security policies, inherit the connection's authentication context, and evade rate limiting. Affected operators should review system configurations, security teams should monitor network traffic, and vulnerability management teams should prioritize patching or mitigating this vulnerability. Asset inventory teams should verify affected systems and ensure that compensating controls are in place while remediation is scheduled and verified. Security teams should also track exceptions, retest remediated assets, and close the item only after evidence is documented. The vulnerability has a high CVSS score of 7.5 and is classified as HIGH severity. Users of OpenSIPS should review and apply patches for OpenSIPS versions 3.6.6 and 4.0.0-rc1, implement compensating controls to detect and prevent SIP message smuggling, and verify system configurations and inventory for potential vulnerabilities.

Vendor: OpenSIPS
Product: Unknown
CVSS: HIGH 7.5
CISA KEV: Not listed in stored evidence
Original CVE published: 2026-08-04
Original CVE updated: 2026-08-05
Advisory published: 2026-08-04
Advisory updated: 2026-08-05

Who should care

Network administrators, security teams, and OpenSIPS users should be aware of this vulnerability and take defensive actions to prevent SIP message smuggling attacks. Affected operators should review system configurations, security teams should monitor network traffic, and vulnerability management teams should prioritize patching or mitigating this vulnerability. Additionally, asset inventory teams should verify affected systems and ensure that compensating controls are in place while remediation is scheduled and verified. Security teams should also track exceptions, retest remediated assets, and close the item only after evidence is documented. This vulnerability has a high CVSS score of 7.5 and is classified as HIGH severity, emphasizing the need for prompt attention and mitigation. Users of OpenSIPS should review and apply patches for OpenSIPS versions 3.6.6 and 4.0.0-rc1, implement compensating controls to detect and prevent SIP message smuggling, and verify system configurations and inventory for potential vulnerabilities. They should also monitor network traffic for suspicious SIP activity and be prepared to respond to potential security incidents related to this vulnerability. The CVE record was published on 2026-08-04T22:17:14.847Z and has not been modified since then, indicating that this vulnerability is actively being monitored and addressed by the CVE community. Users should also consider the potential impact on their systems and take proactive measures to prevent exploitation. This may involve reviewing system configurations, updating software versions, and implementing additional security controls to prevent SIP message smuggling attacks. By taking these steps, users can help protect their systems and prevent potential security incidents related to this vulnerability. The vulnerability affects OpenSIPS versions prior to 3.6.6 and 4.0.0-rc1, and users of these versions should prioritize patching or mitigating this vulnerability to prevent potential security incidents. The vulnerability has been publicly disclosed, and users should be aware of the potential risks and take proactive measures to prevent exploitation. This vulnerability highlights the .

Technical summary

OpenSIPS versions prior to 3.6.6 and 4.0.0-rc1 are vulnerable to SIP message smuggling due to improper parsing of the Content-Length header in the TCP message framing layer. This allows unauthenticated, network-based attackers to smuggle arbitrary SIP messages over TCP-based transports, potentially bypassing front-end SBC/proxy security policies and rate limiting. The vulnerability has been fixed in versions 3.6.6 and 4.0.0-rc1.

Defensive priority

High-priority defensive actions are required to address this vulnerability, as it allows unauthenticated, network-based attackers to smuggle arbitrary SIP messages.

Recommended defensive actions

Review and apply patches for OpenSIPS versions 3.6.6 and 4.0.0-rc1
Implement compensating controls to detect and prevent SIP message smuggling
Monitor network traffic for suspicious SIP activity
Verify system configurations and inventory for potential vulnerabilities
Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed

Evidence notes

OpenSIPS versions prior to 3.6.6 and 4.0.0-rc1 are vulnerable to SIP message smuggling due to improper parsing of the Content-Length header. Evidence from the NVD and CVE.org indicates that this vulnerability allows unauthenticated, network-based attackers to smuggle arbitrary SIP messages over TCP-based transports. Limited details are available on exploitability and affected systems. Defenders should verify system configurations, review network traffic for suspicious SIP activity, and monitor for potential vulnerabilities.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-08-04T22:17:14.847Z and has not been modified since then.