CVE-2026-2967 identifies a security vulnerability in Cesanta Mongoose, a widely used embedded web server and networking library, affecting all versions up to 7.20. The vulnerability arises from improper verification of the source of a communication channel within the TCP Sequence Number Handler, specifically in the getpeer function located in /src/net_builtin.c. This flaw allows an attacker to manipulate the verification process of the communication source, potentially enabling spoofing or unauthorized communication channel establishment. The vulnerability can be exploited remotely without requiring authentication or user interaction, but the attack complexity is high due to the difficulty in crafting a successful exploit. The CVSS 4.0 base score is 6.3, reflecting a medium severity level, with network attack vector, high attack complexity, and no privileges or user interaction needed. Although the vendor was notified early, no patch or response has been provided yet, and no known exploits have been observed in the wild. The vulnerability primarily threatens the integrity of communication channels, possibly allowing attackers to bypass source verification mechanisms, which could lead to unauthorized data injection or manipulation in network communications handled by Mongoose. Given Mongoose’s use in embedded systems, IoT devices, and networked applications, this vulnerability could have broad implications if exploited.

The potential impact of CVE-2026-2967 includes unauthorized manipulation of communication channels handled by Cesanta Mongoose, which could compromise the integrity of data transmitted over these channels. This may allow attackers to inject malicious data, spoof legitimate sources, or disrupt normal communication flows. While confidentiality and availability impacts are limited or not directly indicated, the integrity compromise could affect critical embedded systems and IoT devices relying on Mongoose for network communication. Organizations deploying Mongoose in industrial control systems, smart devices, or network infrastructure could face operational disruptions or data integrity issues. The high complexity and difficult exploitability reduce immediate risk, but the public disclosure and lack of vendor response increase the urgency for mitigation. Without patches, attackers with sufficient skill could develop exploits, especially targeting devices with network exposure. The absence of authentication requirements broadens the attack surface, making remote exploitation feasible in vulnerable environments.

1. Immediate mitigation should focus on network-level controls such as implementing strict firewall rules to limit exposure of devices running Cesanta Mongoose to untrusted networks. 2. Employ network segmentation to isolate vulnerable devices and reduce attack surface. 3. Monitor network traffic for anomalies indicative of spoofing or unauthorized communication attempts targeting Mongoose-based services. 4. Where possible, disable or restrict TCP services provided by Mongoose until a patch is available. 5. Engage in active vulnerability management to track vendor updates or community patches addressing this issue. 6. For embedded or IoT devices, coordinate with device manufacturers or vendors to obtain firmware updates or mitigations. 7. Consider deploying intrusion detection/prevention systems (IDS/IPS) with signatures tuned to detect exploitation attempts targeting TCP sequence verification flaws. 8. Conduct security audits on applications using Mongoose to identify and remediate potential misuse or exposure of vulnerable components. 9. Prepare incident response plans specific to network communication integrity breaches to respond promptly if exploitation is detected.