CVE-2026-2967 Overview
A security vulnerability has been identified in Cesanta Mongoose versions up to 7.20. This vulnerability affects the getpeer function within the file /src/net_builtin.c, specifically in the TCP Sequence Number Handler component. The flaw allows improper verification of the source of a communication channel, potentially enabling attackers to manipulate TCP connections. The vulnerability can be exploited remotely, though the attack complexity is rated as high and exploitability is reported as difficult. A proof-of-concept exploit has been publicly disclosed.
Critical Impact
Attackers could potentially manipulate TCP connections by exploiting improper source verification in the TCP Sequence Number Handler, affecting availability of systems running vulnerable Mongoose versions.
Affected Products
- Cesanta Mongoose versions up to and including 7.20
- Systems using Mongoose embedded web server with TCP networking functionality
- IoT devices and embedded systems utilizing Cesanta Mongoose for network communication
Discovery Timeline
- 2026-02-23 - CVE CVE-2026-2967 published to NVD
- 2026-02-23 - Last updated in NVD database
Technical Details for CVE-2026-2967
Vulnerability Analysis
This vulnerability (CWE-940: Improper Verification of Source of a Communication Channel) exists in the TCP Sequence Number Handler component of Cesanta Mongoose. The flaw resides in the getpeer function located in /src/net_builtin.c, where insufficient validation of communication channel sources can be exploited.
The attack vector is network-based, meaning an adversary can initiate exploitation remotely without requiring authentication or user interaction. However, the high attack complexity and difficult exploitability significantly reduce the practical risk of widespread exploitation. The vulnerability primarily impacts availability, with potential for denial of service conditions.
The vendor (Cesanta) was contacted early during the responsible disclosure process but did not respond, leaving users without an official patch at the time of public disclosure.
Root Cause
The root cause of this vulnerability stems from improper verification mechanisms within the TCP Sequence Number Handler. The getpeer function fails to adequately validate the source of incoming communication channels, allowing an attacker to potentially spoof or manipulate TCP connections. This lack of proper source verification in network protocol handling can lead to connection manipulation attacks.
Attack Vector
The attack is initiated remotely over the network, targeting the TCP stack implementation in Mongoose's built-in networking code. An attacker would need to craft specifically malformed TCP packets or manipulate TCP sequence numbers to exploit this vulnerability. While no authentication or user interaction is required, the high complexity of the attack suggests that successful exploitation requires precise timing and network conditions.
The vulnerability manifests in the boundary handling and source verification logic within the TCP implementation. Technical details and proof-of-concept information can be found in the GitHub CVE Documentation and the GitHub PoC Repository.
Detection Methods for CVE-2026-2967
Indicators of Compromise
- Unusual TCP RST (reset) packets targeting Mongoose-powered services
- Anomalous TCP sequence number patterns in network traffic logs
- Unexpected connection terminations or service availability issues
- Network traffic anomalies suggesting TCP connection manipulation attempts
Detection Strategies
- Monitor network traffic for irregular TCP sequence number behavior targeting Mongoose services
- Implement intrusion detection rules to identify potential TCP manipulation attacks
- Review system logs for unexpected connection resets or network stack errors
- Deploy network-based anomaly detection focused on embedded device communications
Monitoring Recommendations
- Enable verbose logging on systems running Cesanta Mongoose to capture TCP connection events
- Implement network flow monitoring to detect unusual patterns in TCP traffic
- Set up alerts for service availability issues on Mongoose-powered endpoints
- Monitor for publicly available exploit attempts using known PoC techniques
How to Mitigate CVE-2026-2967
Immediate Actions Required
- Inventory all systems running Cesanta Mongoose versions up to 7.20
- Implement network segmentation to limit exposure of vulnerable Mongoose instances
- Deploy network-level protections such as firewalls and intrusion prevention systems
- Monitor vendor channels for official patches or security advisories
Patch Information
As of the last NVD update on 2026-02-23, no official patch has been released by Cesanta. The vendor was contacted during responsible disclosure but did not respond. Organizations should monitor the official Cesanta Mongoose repository and security channels for future updates.
For additional vulnerability intelligence, refer to VulDB #347334 and the VulDB Submission #755450.
Workarounds
- Restrict network access to Mongoose services using firewall rules and access control lists
- Place Mongoose-powered devices behind network security appliances with deep packet inspection
- Consider disabling or limiting TCP functionality if not required for operations
- Implement additional network monitoring to detect exploitation attempts
# Example firewall configuration to restrict access to Mongoose services
# Limit access to trusted IP ranges only
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
