CVE-2019-25038 in Unbound
Summary
by MITRE • 04/27/2021
Unbound before 1.9.5 allows an integer overflow in a size calculation in dnscrypt/dnscrypt.c.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2019-25038 affects the Unbound DNS resolver software version 1.9.5 and earlier, presenting a critical integer overflow condition within the dnscrypt module. This flaw exists in the size calculation logic of the dnscrypt.c file, which handles DNSCrypt protocol implementation for encrypted DNS communications. The vulnerability stems from inadequate input validation and arithmetic overflow handling when processing cryptographic parameters during DNS resolution operations. The integer overflow occurs during the computation of buffer sizes needed for DNSCrypt message handling, potentially leading to memory corruption and system instability.
The technical implementation of this vulnerability involves the manipulation of size calculation parameters that determine memory allocation for DNSCrypt protocol messages. When an attacker crafts malicious DNSCrypt packets with specifically crafted size parameters, the arithmetic operations in the dnscrypt.c module fail to properly validate integer boundaries, resulting in an overflow condition. This overflow can cause subsequent memory allocation operations to use incorrect buffer sizes, potentially leading to buffer overflows, memory corruption, or arbitrary code execution. The flaw aligns with CWE-190, which specifically addresses integer overflow and underflow conditions, and represents a classic example of improper integer handling in security-critical code sections.
The operational impact of CVE-2019-25038 extends beyond simple service disruption to potentially enable remote code execution in vulnerable configurations. Attackers can exploit this vulnerability by sending malicious DNSCrypt packets to Unbound servers, particularly those configured to accept DNSCrypt connections. The vulnerability affects systems where Unbound is deployed as a recursive resolver or forwarder that processes DNSCrypt traffic, making it particularly dangerous for DNS infrastructure providers, enterprise networks, and any organization relying on encrypted DNS resolution. The exploitability of this vulnerability is enhanced when Unbound is configured to use DNSCrypt, as the specific code path involving the integer overflow is activated during DNSCrypt protocol processing.
Organizations should immediately upgrade to Unbound version 1.9.5 or later, which includes patches addressing the integer overflow condition in the dnscrypt.c module. System administrators should also implement network monitoring to detect unusual DNSCrypt traffic patterns that might indicate exploitation attempts. The mitigation strategy should include comprehensive testing of the updated software in staging environments before deployment to production systems. Security teams should consider implementing additional network segmentation and access controls around DNS infrastructure to limit potential attack surface. This vulnerability demonstrates the importance of rigorous input validation in cryptographic implementations and aligns with ATT&CK technique T1071.004 for application layer protocol manipulation, particularly in DNS and DNSCrypt contexts where protocol handling requires precise memory management and integer boundary checks.