CVE-2017-9107 in adns
Summary
by MITRE
An issue was discovered in adns before 1.5.2. It overruns reading a buffer if a domain ends with backslash. If the query domain ended with \, and adns_qf_quoteok_query was specified, qdparselabel would read additional bytes from the buffer and try to treat them as the escape sequence. It would depart the input buffer and start processing many bytes of arbitrary heap data as if it were the query domain. Eventually it would run out of input or find some other kind of error, and declare the query domain invalid. But before then it might outrun available memory and crash. In principle this could be a denial of service attack.
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Analysis
by VulDB Data Team • 05/15/2023
The vulnerability identified as CVE-2017-9107 represents a critical buffer overread flaw in the adns library version 1.5.1 and earlier. This issue manifests when processing DNS queries where the domain name terminates with a backslash character, creating a scenario where the parsing function fails to properly validate buffer boundaries during domain name processing. The adns library, which provides asynchronous DNS resolution capabilities for applications, becomes susceptible to memory corruption when encountering malformed domain names ending with backslash characters. This vulnerability specifically affects the qdparselabel function within the library's DNS parsing implementation, where the absence of proper boundary checking allows the parser to traverse beyond the allocated input buffer.
The technical execution of this vulnerability occurs through the interaction between the backslash termination and the qdparselabel function's handling of quoted query flags. When adns_qf_quoteok_query is specified and a domain name ends with a backslash, the parser attempts to interpret subsequent bytes as escape sequences, causing it to read additional data beyond the intended buffer limits. This behavior creates a scenario where the parser begins processing arbitrary heap data as if it were part of the domain name, leading to unpredictable memory access patterns. The function's failure to properly validate input boundaries results in a classic buffer overread condition that can cause memory corruption and system instability.
The operational impact of CVE-2017-9107 extends beyond simple denial of service to potentially enable more sophisticated attack vectors through memory corruption. While the immediate effect manifests as application crashes due to memory access violations, the vulnerability's potential for exploitation lies in its ability to cause unpredictable behavior that could be leveraged by attackers to execute arbitrary code or cause system instability. The vulnerability maps to CWE-121, which describes stack-based buffer overflow conditions, though this particular case involves heap data corruption rather than stack-based issues. The memory corruption could potentially be exploited to manipulate program execution flow or cause information disclosure through heap spraying techniques.
Mitigation strategies for this vulnerability require immediate patching of the adns library to version 1.5.2 or later, which implements proper buffer boundary checking in the qdparselabel function. System administrators should conduct thorough inventory assessments to identify all applications relying on vulnerable adns versions and ensure timely updates across all affected systems. Network monitoring should be enhanced to detect unusual DNS query patterns that might indicate exploitation attempts targeting this vulnerability. Additionally, input validation should be implemented at the application level to sanitize DNS query inputs before passing them to the adns library, providing defense-in-depth protection. This vulnerability demonstrates the importance of proper input validation and buffer boundary checking in network libraries, aligning with ATT&CK technique T1059.007 for command and script injection through malformed input processing, and highlights the need for comprehensive security testing of parsing functions in network applications.