CVE-2017-13704 in Dnsmasq
Summary
by MITRE
In dnsmasq before 2.78, if the DNS packet size does not match the expected size, the size parameter in a memset call gets a negative value. As it is an unsigned value, memset ends up writing up to 0xffffffff zero's (0xffffffffffffffff in 64 bit platforms), making dnsmasq crash.
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Analysis
by VulDB Data Team • 12/30/2022
The vulnerability identified as CVE-2017-13704 represents a critical buffer over-read condition within the dnsmasq DNS server implementation that can lead to remote denial of service. This flaw exists in dnsmasq versions prior to 2.78 and stems from improper handling of DNS packet size validation during memory allocation operations. The vulnerability manifests when the DNS packet size parameter fails to match expected values, creating a scenario where a negative value is passed to the memset function call. This condition violates fundamental memory safety principles and creates a path for arbitrary code execution or system instability.
The technical root cause of this vulnerability aligns with CWE-128, which describes "Wrap or Overflow" conditions in integer operations. When the size parameter becomes negative due to improper validation, the unsigned integer type in the memset function call transforms this negative value into a massive positive number representing the maximum value for unsigned 32-bit integers, which is 0xffffffff. This transformation causes the memset function to attempt writing an enormous number of bytes to memory, effectively causing a buffer overflow condition that results in memory corruption and system crash. The vulnerability operates at the intersection of memory management and integer overflow concepts, creating a scenario where a simple size validation failure cascades into a catastrophic system failure.
From an operational perspective, this vulnerability presents a significant risk to network infrastructure as it allows remote attackers to trigger denial of service conditions against dnsmasq servers without requiring authentication or specialized privileges. The impact extends beyond simple service disruption as the crash can potentially be exploited to cause more severe system instability or even facilitate further attacks. The vulnerability affects any system running dnsmasq versions before 2.78, making it particularly concerning for network administrators who may have deployed older versions in production environments. The attack vector is straightforward since DNS servers are typically accessible from external networks, making this vulnerability exploitable by any remote attacker with basic network connectivity.
The mitigation strategy for CVE-2017-13704 requires immediate patching of affected dnsmasq installations to version 2.78 or later, which contains the necessary code fixes to properly validate DNS packet sizes before passing them to memory allocation functions. Network administrators should also implement monitoring solutions to detect unusual DNS traffic patterns that might indicate exploitation attempts. The fix addresses the underlying integer overflow condition by ensuring that size parameters are validated against zero before being used in memory operations, preventing the generation of negative values that could cause the memset function to attempt writing excessive memory regions. Additionally, implementing network segmentation and access controls around DNS servers can help limit the potential impact of exploitation attempts while maintaining operational security posture. This vulnerability demonstrates the critical importance of proper input validation and memory safety practices in network infrastructure software, aligning with ATT&CK technique T1499.004 for network denial of service attacks and highlighting the need for robust defensive measures in critical network services.