CVE-2026-102719 in NetX Duo
Summary
by MITRE • 09/29/2026
Predictable DTLS HelloVerifyRequest Cookie in NetX Secure
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability identified as Predictable DTLS HelloVerifyRequest Cookie in NetX Secure represents a critical flaw within the implementation of the Datagram Transport Layer Security protocol, specifically affecting the handshake phase where connection integrity is established. This issue stems from an insufficiently random generation mechanism for the cookie values used during the initial ClientHello and ServerHello exchange. In standard TLS/DTLS operations, servers often employ cookies to mitigate denial-of-service attacks by ensuring that clients have a valid IP address before committing significant computational resources to full handshake processing. However, when these cookies are generated using predictable algorithms or weak entropy sources, they fail to provide the necessary cryptographic assurance of client authenticity and resource allocation control.
From a technical perspective, the core flaw lies in the algorithmic predictability of the HelloVerifyRequest cookie. Instead of utilizing cryptographically secure pseudo-random number generators seeded with high-entropy data from the operating system kernel or hardware random number generators, NetX Secure likely relies on deterministic functions such as linear congruential generators or simple hash-based constructions without adequate salting. This allows an attacker who observes a sequence of cookies to model the underlying generation function and predict future cookie values. The vulnerability is particularly severe in DTLS environments because UDP lacks the inherent connection state tracking of TCP, making it more susceptible to spoofing and amplification attacks if the verification mechanism can be bypassed or predicted.
The operational impact of this weakness extends beyond simple session hijacking. An attacker with knowledge of the cookie generation algorithm can forge valid HelloVerifyRequest responses without needing to receive a legitimate request from the server first. This capability enables several malicious activities, including resource exhaustion attacks where the victim device is forced into processing full handshakes for spoofed connections, effectively turning it into an amplifier in larger distributed denial-of-service campaigns. Furthermore, if session tokens or keys are derived partially based on these predictable cookies, an attacker could potentially reconstruct session states or impersonate legitimate clients to gain unauthorized access to protected resources, compromising the confidentiality and integrity of data transmitted over DTLS channels.
This vulnerability aligns with CWE-330: Use of Insufficiently Random Values, which categorizes flaws where random numbers are used in security-critical contexts but lack sufficient entropy or unpredictability. It also maps closely to MITRE ATT&CK technique T1498: Network Denial of Service, specifically the sub-category involving amplification and reflection attacks facilitated by protocol weaknesses. By exploiting this predictability, adversaries can bypass rate-limiting mechanisms designed to protect network infrastructure from flood-based disruptions, thereby undermining the reliability and availability guarantees provided by secure communication protocols.
Mitigation strategies must focus on strengthening the entropy sources used for cookie generation. Developers should replace any deterministic or weak random number generators with cryptographically strong alternatives that draw from OS-level entropy pools such as /dev/urandom on Unix-like systems or BCryptGenRandom on Windows platforms. Additionally, implementing stateless verification methods that do not rely solely on predictable cookies can enhance resilience against spoofing attacks. Regular security audits and static code analysis focused on cryptographic implementation details are essential to identify similar weaknesses in other components of the NetX Secure suite. Updating to patched versions provided by the vendor is the most immediate remediation step, ensuring that the underlying randomization logic adheres to current best practices for secure protocol implementations.