CVE-2015-3294 in Dnsmasq
Summary
by MITRE
The tcp_request function in Dnsmasq before 2.73rc4 does not properly handle the return value of the setup_reply function, which allows remote attackers to read process memory and cause a denial of service (out-of-bounds read and crash) via a malformed DNS request.
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Analysis
by VulDB Data Team • 05/10/2022
The vulnerability identified as CVE-2015-3294 resides within the Dnsmasq DNS server software, specifically in the tcp_request function where improper handling of the setup_reply function return value creates exploitable conditions. This flaw affects Dnsmasq versions prior to 2.73rc4 and represents a critical security issue that can be leveraged by remote attackers to extract sensitive process memory information and potentially cause system crashes. The vulnerability manifests when processing malformed DNS requests over TCP connections, where the software fails to properly validate or check the return values from internal functions, leading to unpredictable behavior in memory access patterns.
The technical root cause of this vulnerability stems from inadequate error handling within the TCP request processing pipeline of Dnsmasq. When the setup_reply function is invoked during DNS response construction, it may return error codes or specific values that indicate failure conditions or special states. However, the tcp_request function does not properly evaluate these return values before proceeding with memory operations, particularly in scenarios involving out-of-bounds memory reads. This improper validation creates a path where attackers can craft specially malformed DNS packets that trigger the vulnerable code path, causing the software to attempt memory access beyond legitimate boundaries.
From an operational impact perspective, this vulnerability enables attackers to perform out-of-bounds memory reads that can expose sensitive information contained within the Dnsmasq process memory space. This includes potentially confidential data such as cryptographic keys, user credentials, or internal system information that could be leveraged for further exploitation. The vulnerability also creates conditions for denial of service attacks, where carefully crafted malformed requests can cause the Dnsmasq process to crash or become unresponsive, effectively disrupting DNS resolution services for legitimate network users. The combination of information disclosure and availability impact makes this vulnerability particularly dangerous in network infrastructure environments.
The exploitation of CVE-2015-3294 aligns with several ATT&CK techniques including T1071.004 Application Layer Protocol DNS and T1499.004 Endpoint Denial of Service, as attackers can leverage DNS protocol weaknesses to cause service disruption and information leakage. This vulnerability also maps to CWE-125 Out-of-bounds Read, which is classified under the Common Weakness Enumeration framework for memory safety issues. The flaw demonstrates poor defensive programming practices where return value validation is insufficient, creating opportunities for attackers to manipulate program flow through carefully crafted inputs. Organizations using Dnsmasq in production environments should prioritize patching to version 2.73rc4 or later, as this release includes proper return value handling and memory access validation that prevents the exploitation conditions described in this vulnerability.
Security practitioners should consider implementing network monitoring to detect unusual DNS traffic patterns that might indicate exploitation attempts, particularly focusing on malformed TCP DNS requests. The vulnerability also highlights the importance of input validation and proper error handling in network services, as similar issues could exist in other components of the DNS infrastructure. Organizations should also review their DNS server configurations and ensure proper access controls are in place to limit exposure to potentially malicious actors. The remediation process requires careful consideration of the patch deployment timing, as Dnsmasq serves critical network functions, and any disruption to DNS services could impact overall network operations. Additionally, the vulnerability demonstrates the need for regular security audits of network infrastructure components to identify and address similar memory safety issues that could be exploited in similar network services.