CVE-2026-13002: 
dnsmasq vulnerability analysis and mitigation

CVE-2026-13002 is a Denial of Service vulnerability in the dnsmasq DNS/DHCP service caused by an infinite loop flaw in the dnssec.c library during DNSSEC NSEC/NSEC3 type bitmap parsing. An attacker who controls any DNSSEC-signed zone can send a single crafted DNS response to hang the dnsmasq process, effectively killing all DNS resolution for its clients. Affected products include dnsmasq as shipped with Red Hat Enterprise Linux 6.0, 7.0, 8.0, 9.0, 10.0, and Red Hat OpenShift Container Platform 4.x. The vulnerability was reported on June 8, 2026, and publicly disclosed on August 14, 2026, with a CVSS v3.1 base score of 4.4 (Medium) (Red Hat CVE, Github Advisory).

The root cause is classified as CWE-835 (Loop with Unreachable Exit Condition / Infinite Loop) within the dnssec.c library of dnsmasq, specifically during parsing of DNSSEC NSEC/NSEC3 type bitmaps in DNS responses. An attacker who controls a DNSSEC-signed zone can craft a malicious DNS response that triggers the infinite loop, causing the dnsmasq process to consume CPU resources indefinitely without terminating. Exploitation requires the attacker to control a DNSSEC-signed zone and have the ability to respond to DNS queries from the target dnsmasq instance (e.g., via a rogue authoritative nameserver or DNS poisoning). The vulnerability was reported by Lennart Espe and tracked internally as Red Hat Bugzilla #2486360 (Red Hat CVE, Red Hat Bugzilla).

Successful exploitation results in a complete Denial of Service of the dnsmasq process, halting all DNS resolution for every client relying on the affected instance. There is no confidentiality or integrity impact — the vulnerability is purely an availability issue. In environments where dnsmasq serves as the primary DNS resolver (e.g., embedded systems, container platforms, or RHEL deployments with DNSSEC enabled), this can cause widespread network disruption for all connected clients (Red Hat CVE, Github Advisory).

There is no public proof-of-concept exploit code and no evidence of active in-the-wild exploitation as of the disclosure date (Github Advisory). The EPSS score is approximately 0.108% (1st percentile), indicating a low near-term exploitation probability. The NVD SSVC assessment classifies the vulnerability as non-automatable with partial technical impact. The CVE is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Exploitation requires the attacker to control a DNSSEC-signed zone, which limits the attack surface compared to fully unauthenticated, network-accessible vulnerabilities (Red Hat CVE).

1. Reconnaissance: Identify target systems running dnsmasq with DNSSEC validation enabled (e.g., via network scanning or DNS probing to detect dnsmasq version banners).
2. Establish a DNSSEC-signed zone: The attacker must control an authoritative DNS zone that is properly DNSSEC-signed, or be in a position to inject crafted DNSSEC responses (e.g., via DNS cache poisoning or a rogue resolver).
3. Craft a malicious DNSSEC response: Construct a DNS response containing a specially crafted NSEC or NSEC3 record with a malformed type bitmap that triggers the infinite loop condition in dnssec.c.
4. Deliver the crafted response: Cause the target dnsmasq instance to query the attacker-controlled zone (e.g., by inducing a client to resolve a hostname in the malicious zone), so dnsmasq receives and processes the crafted DNSSEC response.
5. Trigger the infinite loop: The malformed NSEC/NSEC3 type bitmap causes dnsmasq's parsing logic to enter an infinite loop, consuming all available CPU and hanging the process.
6. Achieve DoS: The dnsmasq process becomes unresponsive, stopping all DNS resolution for clients that depend on it until the process is manually restarted (Red Hat CVE, Red Hat Bugzilla).

• Process: The dnsmasq process consuming 100% CPU on a single core for an extended period without returning to normal; process appears running but unresponsive to DNS queries.
• Network: DNS queries from clients going unanswered; timeouts on DNS resolution across all clients served by the affected dnsmasq instance; unusual NSEC/NSEC3 responses from external or unexpected authoritative nameservers in DNS traffic captures.
• Logs: System logs (e.g., /var/log/messages or journalctl) showing dnsmasq becoming unresponsive or watchdog/service manager reporting dnsmasq failures; absence of new dnsmasq query log entries despite client activity.
• System: High CPU utilization attributed to the dnsmasq PID visible via top or ps; service monitoring alerts for DNS resolution failures or dnsmasq process health checks.

Red Hat has confirmed that no effective mitigation is currently available that meets its criteria for ease of use, deployment, and stability — the dnsmasq component is required for installations using DNSSEC (Red Hat CVE). A patch is available via the GitHub Advisory (GHSA-gf7x-hg8h-x3gf); users should apply vendor-provided security updates as they become available for their specific RHEL or OpenShift version (Github Advisory). As interim measures, consider: (1) disabling DNSSEC validation in dnsmasq if your threat model permits, (2) implementing network-level filtering to restrict DNSSEC responses from untrusted or unexpected zones, and (3) configuring process supervision (e.g., systemd watchdog) to automatically restart dnsmasq if it becomes unresponsive. Amazon Linux 2 users can refer to the ALAS2DNSMASQ-2026-004 advisory for platform-specific guidance.

Red Hat acknowledged the vulnerability and credited Lennart Espe for the responsible disclosure (Red Hat CVE). The GitHub Advisory Database classified the severity as Moderate, consistent with the CVSS 4.4 score (Github Advisory). No significant broader community discussion or media coverage has been identified beyond standard vulnerability database entries and scanner plugin updates (Nessus plugin 335458).