CVE-2019-25034 in Unbound
Summary
by MITRE • 04/27/2021
Unbound before 1.9.5 allows an integer overflow in sldns_str2wire_dname_buf_origin, leading to an out-of-bounds write.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2019-25034 represents a critical integer overflow condition within the Unbound DNS resolver software version 1.9.5 and earlier. This flaw exists in the sldns_str2wire_dname_buf_origin function which processes domain name strings during DNS message conversion from text to wire format. The integer overflow occurs when handling certain malformed domain name inputs that exceed the expected buffer boundaries, creating a scenario where the application attempts to write data beyond the allocated memory space. This particular vulnerability falls under the CWE-190 category of integer overflow, specifically manifesting as an out-of-bounds write condition that can lead to arbitrary code execution or service disruption.
The technical implementation of this vulnerability involves the manipulation of domain name parsing logic within the DNS resolver's string conversion routines. When Unbound processes domain names with specific malformed characteristics, the internal counter or size calculation used to determine buffer allocation becomes corrupted due to integer overflow. This overflow causes subsequent memory operations to write data beyond the intended buffer boundaries, potentially overwriting adjacent memory regions including critical program structures, return addresses, or other sensitive data. The vulnerability is particularly dangerous because it can be triggered through DNS queries containing specially crafted domain names, making it exploitable in network-based attacks against DNS resolver services.
The operational impact of CVE-2019-25034 extends beyond simple service disruption to potentially enable remote code execution capabilities for attackers. An attacker who can control the input to the vulnerable function can craft malicious DNS queries that trigger the integer overflow condition, leading to memory corruption that may allow arbitrary code execution on the target system. This vulnerability affects DNS resolver implementations that rely on the sldns library for domain name processing, potentially impacting a wide range of network infrastructure including authoritative servers, recursive resolvers, and caching systems. The out-of-bounds write condition creates opportunities for attackers to manipulate program flow, inject malicious code, or cause denial of service conditions that can persist until the affected software is patched.
Mitigation strategies for this vulnerability primarily focus on immediate software updates to Unbound version 1.9.5 or later where the integer overflow has been addressed through proper input validation and boundary checking. System administrators should prioritize patching affected DNS resolver installations and implement network monitoring to detect unusual DNS query patterns that might indicate exploitation attempts. Additional defensive measures include configuring DNS resolvers with strict input validation, implementing rate limiting for DNS queries, and deploying intrusion detection systems that can identify malformed DNS traffic patterns. The vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol usage and T1499.004 for network denial of service, making it relevant to both defensive security operations and incident response procedures. Organizations should also consider implementing network segmentation and access controls to limit exposure of vulnerable DNS services to untrusted networks and users.