CVE-2017-9109 in adns
Summary
by MITRE
An issue was discovered in adns before 1.5.2. It fails to ignore apparent answers before the first RR that was found the first time. when this is fixed, the second answer scan finds the same RRs at the first. Otherwise, adns can be confused by interleaving answers for the CNAME target, with the CNAME itself. In that case the answer data structure (on the heap) can be overrun. With this fixed, it prefers to look only at the answer RRs which come after the CNAME, which is at least arguably correct.
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Analysis
by VulDB Data Team • 05/15/2023
The vulnerability identified in adns version 1.5.1 and earlier represents a critical heap buffer overflow condition that stems from improper handling of DNS response parsing during asynchronous DNS resolution operations. This flaw specifically manifests when processing DNS responses that contain CNAME records, where the library fails to properly distinguish between different response sections and maintains an inconsistent state during multiple scan passes through the DNS answer data. The issue occurs because adns does not correctly ignore apparent answers that appear before the first valid resource record during its initial scan, creating a scenario where subsequent scans process duplicate data structures and potentially overwrite heap memory. This behavior directly violates the fundamental principles of memory safety and proper data structure management that are essential for robust network resolution libraries. The vulnerability falls under the CWE-121 heap-based buffer overflow category, which represents one of the most dangerous classes of memory corruption flaws that can lead to arbitrary code execution.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable remote code execution attacks against systems that rely on adns for DNS resolution. When processing DNS responses containing CNAME records, the library's failure to properly manage its internal data structures can cause the heap-based answer data structures to be overrun with data from interleaved DNS response sections. This creates a situation where attackers can craft malicious DNS responses that, when processed by vulnerable adns implementations, will cause the library to write beyond allocated memory boundaries. The attack vector becomes particularly concerning because DNS resolution is a fundamental operation in network communications, making this vulnerability exploitable in numerous contexts including web browsers, email clients, and network services that depend on asynchronous DNS resolution. The flaw is particularly dangerous because it can be triggered by any DNS response containing CNAME records, making it difficult to predict or prevent in complex network environments. This vulnerability aligns with ATT&CK technique T1059.007 for command and script interpreter execution, as successful exploitation could allow attackers to execute arbitrary code through heap corruption.
The fix implemented in adns version 1.5.2 addresses the root cause by changing the library's behavior to prefer scanning only the answer RRs that come after the CNAME record, which is a more logical approach to DNS response processing. This change ensures that the library maintains a consistent state during multiple scan passes and prevents the duplication of processing that leads to heap overruns. The solution represents a proper implementation of the DNS response parsing protocol where the library correctly separates the processing of CNAME records from the processing of the target records, eliminating the possibility of interleaved data corruption. This approach aligns with security best practices for memory management and demonstrates proper defensive programming techniques that should be applied to all network protocol libraries. The mitigation strategy involves updating to adns version 1.5.2 or later, which contains the necessary patches to prevent the heap buffer overflow condition from occurring. Organizations should also implement network monitoring to detect potential exploitation attempts through malformed DNS responses and consider deploying intrusion detection systems that can identify suspicious DNS traffic patterns that might indicate an active exploitation attempt.