CVE-2019-25033 in Unbound
Summary
by MITRE • 04/27/2021
Unbound before 1.9.5 allows an integer overflow in the regional allocator via the ALIGN_UP macro.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2019-25033 represents a critical integer overflow issue within the Unbound DNS resolver software version 1.9.5 and earlier. This flaw exists in the regional allocator component of the software, which is responsible for managing memory allocation during DNS query processing. The vulnerability specifically manifests through the ALIGN_UP macro, a fundamental memory alignment utility that calculates memory block boundaries. When processing certain malformed DNS responses or crafted payloads, the ALIGN_UP macro fails to properly validate integer inputs, leading to arithmetic overflow conditions that can result in unpredictable memory behavior.
The technical implementation of this vulnerability stems from improper handling of integer arithmetic within the memory allocation subsystem. The ALIGN_UP macro, designed to ensure memory blocks are properly aligned for optimal performance, performs calculations that can exceed the maximum representable value for the integer type being used. This occurs when the macro processes large or malformed input values that, when subjected to alignment calculations, cause the integer to wrap around to a much smaller value. Such overflow conditions can potentially lead to memory corruption, where adjacent memory regions become overwritten or improperly accessed. The vulnerability is particularly concerning because it operates at the memory management layer, making it a prime target for exploitation that could result in denial of service or potentially arbitrary code execution depending on the specific context of memory corruption.
The operational impact of this vulnerability extends across multiple security domains and deployment scenarios where Unbound DNS resolver is utilized. Organizations relying on Unbound for DNS resolution, particularly those operating in high-traffic environments or serving as authoritative name servers, face significant risk from this integer overflow. The vulnerability can be exploited through carefully crafted DNS responses that trigger the problematic memory alignment calculations, potentially leading to service disruption or system instability. Given that DNS resolvers are fundamental infrastructure components, exploitation of this vulnerability could affect broader network operations and potentially enable more sophisticated attacks such as cache poisoning or denial of service against critical services. The vulnerability's presence in the regional allocator means that any DNS query processing that involves memory allocation could potentially be affected, making it a systemic risk rather than a limited scope issue.
Mitigation strategies for CVE-2019-25033 primarily focus on upgrading to Unbound version 1.9.5 or later, where the integer overflow has been addressed through proper input validation and arithmetic overflow protection mechanisms. Organizations should implement immediate patch management procedures to ensure all instances of Unbound are updated to secure versions. Additional protective measures include implementing network segmentation to limit exposure of DNS resolver services, deploying intrusion detection systems to monitor for anomalous DNS traffic patterns, and establishing robust monitoring protocols to detect potential exploitation attempts. Security teams should also consider implementing input validation at network boundaries to filter out malformed DNS responses that could trigger the vulnerability. This vulnerability aligns with CWE-190, Integer Overflow or Wraparound, and could potentially map to ATT&CK technique T1071.004 for application layer protocol manipulation. Organizations should conduct thorough security assessments to verify that all DNS infrastructure components have been properly updated and validated to prevent exploitation of this memory management vulnerability.