Out-of-Bounds Read in Dnsmasq DNS Response Parsing

Executive Summary

CVE-2026-12969 is an out-of-bounds read vulnerability in dnsmasq's find_soa() function located in src/rfc1035.c. The problem occurs when parsing NS section records in NXDOMAIN or NODATA DNS responses. The function extract_name() is called with extrabytes=0, which only checks if the DNS name fits within the packet but fails to verify that 10 additional bytes exist for fixed-length DNS record fields such as type, class, TTL, and rdlen.

Because of this, the code reads 10 bytes beyond the valid packet boundary unconditionally, potentially accessing stale heap data from previous DNS transactions. An attacker controlling a DNS zone can exploit this by sending a specially crafted NXDOMAIN response that causes this out-of-bounds read.

Although the over-read usually stays within dnsmasq's over-allocated packet buffer, reducing the chance of a crash, it still exposes data outside the logical packet boundary.

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Impact Analysis

This vulnerability allows a remote attacker who controls a DNS zone to cause dnsmasq to read 10 bytes beyond the intended packet boundary, potentially exposing stale heap data from previous DNS transactions.

While the risk of a crash is low due to dnsmasq's over-allocated buffer, the exposure of stale data could lead to information disclosure, which might be leveraged in further attacks depending on the nature of the leaked data.

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Mitigation Strategies

The vulnerability in dnsmasq's find_soa() function was fixed in dnsmasq version 2.93rc1.

To mitigate this vulnerability, you should upgrade dnsmasq to version 2.93rc1 or later.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Detection Guidance

This vulnerability involves an out-of-bounds read in dnsmasq's find_soa() function when processing crafted NXDOMAIN responses with specific NS section records. Detection typically involves verifying the dnsmasq version and monitoring for suspicious DNS responses that could exploit this flaw.

To detect if your system is vulnerable, first check the installed dnsmasq version. Versions prior to 2.93rc1 are affected.

• Check dnsmasq version: `dnsmasq --version`
• Monitor DNS traffic for unusual NXDOMAIN responses with NS records that might be crafted to exploit this vulnerability using packet capture tools like tcpdump or Wireshark.
• Example tcpdump command to capture DNS traffic: `tcpdump -i <interface> port 53 -w dns_traffic.pcap`
• Analyze captured traffic with Wireshark to inspect NXDOMAIN responses and NS records for anomalies.

No specific detection commands or signatures for this vulnerability are provided in the available resources, so detection relies on version checking and traffic analysis.

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