CVE-2025-2962: Zephyr Project DNS DoS Vulnerability

CVE-2025-2962 Overview

CVE-2025-2962 is a denial-of-service vulnerability in the DNS implementation of the Zephyr Real-Time Operating System (RTOS). The flaw allows remote attackers to trigger an infinite loop condition (CWE-835) in the DNS resolution code, causing affected devices to become unresponsive. This vulnerability is particularly concerning for IoT and embedded systems that rely on Zephyr for real-time operations, as a successful attack could render critical infrastructure unavailable.

Critical Impact

Remote attackers can exploit this vulnerability over the network without authentication to cause complete denial of service on Zephyr-based IoT devices and embedded systems by triggering an infinite loop in DNS processing.

Affected Products

• Zephyrproject Zephyr RTOS (all versions prior to patch)
• IoT devices and embedded systems running vulnerable Zephyr firmware
• Industrial and consumer devices utilizing Zephyr's DNS client implementation

Discovery Timeline

• 2025-06-24 - CVE-2025-2962 published to NVD
• 2025-10-30 - Last updated in NVD database

Technical Details for CVE-2025-2962

Vulnerability Analysis

This vulnerability resides in Zephyr's DNS implementation and is classified as CWE-835 (Loop with Unreachable Exit Condition). The flaw occurs when the DNS parsing code encounters specially crafted DNS response packets that cause the parsing logic to enter a loop condition from which it cannot exit.

The vulnerability is remotely exploitable over the network without requiring any privileges or user interaction. While the vulnerability does not impact confidentiality or integrity, it has a severe impact on availability, making it a significant concern for IoT deployments where device uptime is critical.

Embedded systems and IoT devices running Zephyr are particularly vulnerable because they often operate in environments where continuous availability is essential, such as industrial control systems, medical devices, and smart home infrastructure.

Root Cause

The root cause of this vulnerability is an infinite loop condition (CWE-835) in the DNS packet parsing logic. When processing DNS responses, the code fails to properly handle certain malformed or edge-case packet structures, causing the parser to loop indefinitely without reaching a termination condition.

This type of vulnerability typically occurs when:

• Loop termination conditions do not account for all possible input states
• Pointer or offset calculations within the DNS parsing logic fail to advance properly
• Malformed DNS compression pointers create circular references that the parser follows indefinitely

Attack Vector

The attack vector for CVE-2025-2962 is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Positioning themselves to intercept DNS traffic (man-in-the-middle) or by controlling a malicious DNS server
2. Sending a specially crafted DNS response packet to a vulnerable Zephyr device
3. The malformed packet triggers the infinite loop condition in the DNS parsing code
4. The device becomes unresponsive as the CPU is consumed by the infinite loop

The vulnerability manifests in the DNS response handling code. When a Zephyr device performs a DNS query and receives a maliciously crafted response, the parsing logic enters an infinite loop, consuming CPU resources and effectively causing a denial of service. For detailed technical information, refer to the GitHub Security Advisory for GHSA-2qp5-c2vq-g2ww.

Detection Methods for CVE-2025-2962

Indicators of Compromise

• Zephyr-based devices becoming unresponsive or timing out during DNS resolution operations
• Abnormally high CPU utilization on embedded devices without corresponding legitimate workload
• Network logs showing DNS query requests without corresponding successful resolutions
• Device watchdog timer triggers or system resets following DNS activity

Detection Strategies

• Monitor network traffic for anomalous DNS response packets targeting Zephyr devices
• Implement DNS traffic inspection at network boundaries to identify malformed responses
• Deploy intrusion detection rules to flag unusual DNS packet structures or compression pointer patterns
• Use SentinelOne Singularity to monitor IoT and embedded device behavior for signs of resource exhaustion attacks

Monitoring Recommendations

• Enable logging on DNS proxy servers and firewalls to capture DNS transaction details
• Configure alerting for Zephyr devices that stop responding to health checks following DNS activity
• Implement network segmentation to isolate IoT devices and limit exposure to potential DNS-based attacks
• Review DNS server logs for unusual query patterns or responses targeting specific device types

How to Mitigate CVE-2025-2962

Immediate Actions Required

• Identify all Zephyr-based devices in your environment and assess their firmware versions
• Apply the security patch from the Zephyr project as soon as it becomes available for your deployment
• Consider implementing network-level DNS filtering to inspect and sanitize DNS responses before they reach vulnerable devices
• Isolate vulnerable IoT devices on separate network segments with restricted DNS access

Patch Information

The Zephyr project has addressed this vulnerability. Review the GitHub Security Advisory GHSA-2qp5-c2vq-g2ww for specific patch details and affected version information. Organizations should update to the patched Zephyr version and rebuild firmware for affected devices.

Workarounds

• Deploy a trusted DNS proxy or resolver that validates and sanitizes DNS responses before forwarding to IoT devices
• Implement network access controls to ensure Zephyr devices only communicate with known, trusted DNS servers
• Use firewall rules to block DNS responses from untrusted sources reaching vulnerable device networks
• Consider implementing a local caching DNS server with strict response validation for IoT network segments

# Example: Firewall rule to restrict DNS access for IoT devices
# Only allow DNS queries to trusted internal DNS server (192.168.1.53)
iptables -A FORWARD -s 192.168.10.0/24 -p udp --dport 53 ! -d 192.168.1.53 -j DROP
iptables -A FORWARD -s 192.168.10.0/24 -p tcp --dport 53 ! -d 192.168.1.53 -j DROP