CVE-2026-51603 in CP3 V3.0
Summary
by MITRE • 07/09/2026
A stack-based buffer overflow vulnerability in the RTSP service of Tenda CP3 V3.0 (firmware V31.1.9.91) allows an unauthenticated remote attacker to cause a denial of service via a crafted second SETUP request. After completing the OPTIONS, DESCRIBE, and a legitimate first SETUP request to obtain a valid session ID, the RTSP service's second-stage URL routing parser fails to validate the length of the URL field in the subsequent SETUP request. By supplying a URL consisting of exactly four consecutive repetitions of a valid RTSP URL, an attacker can bypass first-stage format validation and trigger a stack buffer overflow, causing an immediate crash of the RTSP service process and rendering the device inaccessible to all clients on the local network.
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Analysis
by VulDB Data Team • 07/09/2026
This vulnerability represents a critical stack-based buffer overflow in the RTSP service component of Tenda CP3 V3.0 firmware version V31.1.9.91, classified under CWE-121 as a stack-based buffer overflow due to inadequate input validation in the second-stage URL parsing logic. The flaw occurs specifically within the RTSP service's handling of SETUP requests, where the initial validation stages permit a malicious payload to pass through while the subsequent URL routing parser fails to enforce proper length constraints on the URL field. The vulnerability exploits the device's RTSP implementation by requiring an attacker to first establish a legitimate session through OPTIONS, DESCRIBE, and a valid first SETUP request to obtain a valid session ID before proceeding with the malicious second SETUP request that triggers the overflow condition.
The technical exploitation mechanism relies on the precise construction of a URL field containing exactly four consecutive repetitions of a valid RTSP URL structure. This specific pattern bypasses the first-stage format validation by maintaining syntactic correctness while exceeding the allocated stack buffer boundaries during the second-stage parsing. The vulnerability's design allows for remote code execution potential through process crash conditions that can be leveraged for persistent denial of service attacks against legitimate network services. The attack vector requires no authentication credentials and operates over the standard RTSP protocol port, making it particularly dangerous for devices deployed in residential or enterprise environments where such services may be exposed to untrusted networks.
The operational impact of this vulnerability extends beyond simple service disruption as it creates a persistent denial of service condition that renders the entire device inaccessible to network clients. The immediate crash of the RTSP service process affects not only media streaming capabilities but also potentially impacts other network functions dependent on the same service framework. Network administrators face significant challenges in mitigating this vulnerability since the attack can be executed without any prior authentication, making it an ideal candidate for automated exploitation campaigns targeting embedded devices with exposed RTSP services. The flaw demonstrates poor input validation practices and highlights the importance of implementing robust bounds checking mechanisms in network protocol parsers.
Mitigation strategies should focus on firmware updates from Tenda to address the specific buffer overflow condition in the RTSP service implementation, while network segmentation can provide temporary protection by isolating affected devices from critical network segments. Network administrators should consider disabling RTSP services entirely if they are not required for legitimate operations, as this removes the attack surface entirely. Additional protective measures include implementing network intrusion detection systems to monitor for anomalous RTSP traffic patterns and deploying application layer firewalls that can filter malformed SETUP requests before they reach vulnerable components. The vulnerability aligns with ATT&CK technique T1203 (Exploitation for Client Execution) and represents a common pattern of insufficient input validation in embedded device firmware that has been documented across multiple vendors, emphasizing the need for comprehensive security testing throughout the software development lifecycle.
The technical flaw demonstrates a fundamental lack of proper bounds checking in the RTSP service's URL field handling mechanism, where the second-stage parser fails to validate that the URL length does not exceed allocated buffer space. This represents a classic example of how layered validation approaches can be circumvented when early stages permit malicious data structures to pass through while later stages fail to enforce proper size constraints. The vulnerability's exploitation requires minimal technical skill and can be automated, making it particularly attractive for botnet operators seeking to compromise large numbers of embedded devices. Security researchers should monitor for similar patterns in other firmware implementations that handle RTSP or similar streaming protocols, as this type of vulnerability often indicates broader architectural issues in embedded system security design. The attack's ability to cause immediate process termination without requiring complex exploitation techniques makes it a particularly effective denial of service mechanism that can be combined with other attacks for more sophisticated compromise scenarios.