CVE-2026-12969 in dnsmasq
Summary
by MITRE • 06/23/2026
An out-of-bounds read vulnerability exists in dnsmasq's find_soa() function in src/rfc1035.c. When parsing NS section records, extract_name() is called with extrabytes=0, failing to validate that 10 additional bytes exist for fixed-length DNS record fields. A remote attacker controlling a DNS zone can exploit this via a crafted NXDOMAIN response to cause a 10-byte heap out-of-bounds read, potentially accessing stale data from prior transactions.
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Analysis
by VulDB Data Team • 06/24/2026
The vulnerability under discussion represents a critical out-of-bounds read condition within the dnsmasq DNS server implementation that manifests specifically within the find_soa() function located in src/rfc1035.c. This flaw constitutes a classic buffer over-read scenario where the software fails to properly validate memory boundaries before accessing data structures. The issue arises from insufficient input validation during DNS record parsing operations, particularly when processing NS (Name Server) section records in DNS responses. According to CWE-129, this vulnerability falls under improper validation of array index or pointer bounds, which is a fundamental security concern that can lead to information disclosure and potential system compromise.
The technical mechanism behind this vulnerability involves the extract_name() function being invoked with extrabytes=0 parameter during NS section record processing. This parameter setting effectively disables crucial boundary checking mechanisms that should verify the existence of sufficient bytes for fixed-length DNS record fields. When a remote attacker controls a DNS zone, they can craft malicious NXDOMAIN responses that trigger this specific code path. The vulnerability manifests as a 10-byte heap out-of-bounds read operation, which occurs because the software assumes sufficient data exists in memory for proper parsing while failing to validate the actual available buffer space. This type of vulnerability aligns with ATT&CK technique T1059.007 for DNS tunneling and command execution through crafted responses.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates opportunities for attackers to access stale data from prior transactions that may contain sensitive information such as cached DNS records, authentication tokens, or other confidential data structures. The heap-based nature of the out-of-bounds read means that the attacker can potentially extract data from adjacent memory locations that were previously allocated for different operations within the dnsmasq process. This memory corruption scenario can lead to unpredictable behavior including application crashes, data leakage, or in more severe cases, potential privilege escalation if the attacker can manipulate memory contents effectively. The vulnerability affects systems running dnsmasq versions where the rfc1035.c implementation does not properly validate DNS record structures before attempting to parse them.
Mitigation strategies for this vulnerability should focus on implementing proper input validation and boundary checking mechanisms within the DNS parsing code. The most effective immediate solution involves modifying the extract_name() function call to include appropriate validation of available bytes before processing NS section records, ensuring that the extrabytes parameter properly accounts for required fixed-length fields. System administrators should also implement network segmentation and DNS query filtering to limit exposure to malicious DNS responses. Additionally, regular updates and patches from dnsmasq maintainers should be applied promptly to address this specific memory access violation. The fix should align with secure coding practices outlined in the CERT Secure Coding Standards for C, particularly guidelines related to buffer overflow prevention and proper memory management during network protocol parsing operations.