CVE-2016-7069 in dnsdist
Summary
by MITRE
An issue has been found in dnsdist before 1.2.0 in the way EDNS0 OPT records are handled when parsing responses from a backend. When dnsdist is configured to add EDNS Client Subnet to a query, the response may contain an EDNS0 OPT record that has to be removed before forwarding the response to the initial client. On a 32-bit system, the pointer arithmetic used when parsing the received response to remove that record might trigger an undefined behavior leading to a crash.
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Analysis
by VulDB Data Team • 05/08/2023
The vulnerability identified as CVE-2016-7069 represents a critical buffer overflow condition affecting dnsdist versions prior to 1.2.0, specifically manifesting when processing EDNS0 OPT records in DNS responses from backend servers. This flaw occurs within the DNS distribution server's handling of EDNS Client Subnet functionality, where dnsdist is configured to add client subnet information to outgoing queries. The system's response processing mechanism attempts to strip the EDNS0 OPT record from backend responses before forwarding them to original clients, creating a potential attack surface through malformed pointer arithmetic operations.
The technical implementation of this vulnerability stems from improper pointer handling during the parsing of DNS response packets on 32-bit architectures. When dnsdist processes responses containing EDNS0 OPT records, it employs pointer arithmetic to locate and remove these records before forwarding the response. On 32-bit systems, the specific arithmetic operations used in this parsing routine can result in undefined behavior due to integer overflow or improper memory access patterns. This undefined behavior manifests as memory corruption that ultimately leads to a segmentation fault and subsequent application crash, effectively causing a denial of service condition.
The operational impact of CVE-2016-7069 extends beyond simple service disruption, as it represents a remote code execution vector that could be exploited by malicious actors to compromise DNS infrastructure. The vulnerability affects systems running dnsdist in environments where EDNS Client Subnet functionality is enabled, which is common in modern DNS deployments for privacy and performance optimization. Attackers could craft specially malformed DNS responses containing crafted OPT records that, when processed by vulnerable dnsdist instances, would trigger the exploitable pointer arithmetic and cause system crashes. This vulnerability directly aligns with CWE-121, heap-based buffer overflow, and maps to ATT&CK technique T1499.004 for network denial of service attacks.
Mitigation strategies for this vulnerability require immediate patching of dnsdist installations to version 1.2.0 or later, where the problematic pointer arithmetic has been corrected and memory safety mechanisms have been implemented. Organizations should also consider implementing network segmentation and access controls to limit exposure of dnsdist servers to untrusted networks. Additionally, monitoring systems should be configured to detect unusual crash patterns or service disruptions that might indicate exploitation attempts. The fix addresses the underlying memory management issues by implementing proper bounds checking and safe pointer operations during DNS response parsing, preventing the undefined behavior that previously led to system instability and potential exploitation.