CVE-2018-20994 in trust-dns-proto Crate
Summary
by MITRE
An issue was discovered in the trust-dns-proto crate before 0.5.0-alpha.3 for Rust. There is infinite recursion because DNS message compression is mishandled.
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Analysis
by VulDB Data Team • 12/04/2023
The vulnerability identified as CVE-2018-20994 resides within the trust-dns-proto crate, a critical component in Rust-based DNS protocol implementations that handles DNS message parsing and serialization. This issue manifests as a denial-of-service condition through infinite recursion, fundamentally undermining the stability and reliability of systems relying on this crate for DNS operations. The vulnerability specifically affects versions prior to 0.5.0-alpha.3, indicating that developers using older iterations of this crate were exposed to potential exploitation scenarios that could disrupt normal service operations.
The technical root cause of this vulnerability stems from improper handling of DNS message compression mechanisms during the parsing process. DNS message compression is a standard technique used to reduce message size by replacing repeated domain names with pointers to their first occurrence within the message. The trust-dns-proto crate fails to properly validate or limit the recursion depth when processing compressed DNS messages, allowing maliciously crafted DNS responses to contain circular references that cause the parser to enter infinite recursive loops. This flaw represents a classic example of insufficient input validation and lacks proper recursion depth checking mechanisms that should be implemented when processing structured data formats.
From an operational impact perspective, this vulnerability creates significant risks for systems that process DNS messages, particularly those serving as DNS resolvers, forwarders, or authoritative servers. An attacker could craft a specially formatted DNS response containing compressed data with circular references, causing any system using the vulnerable crate to consume excessive CPU resources and potentially crash or become unresponsive. The infinite recursion consumes system resources rapidly and can be exploited to perform resource exhaustion attacks against DNS services, effectively creating a denial-of-service condition that impacts legitimate users and network operations. This vulnerability particularly affects applications that handle external DNS traffic or those that perform extensive DNS message processing, making it a critical concern for network infrastructure providers.
The vulnerability aligns with CWE-674, which addresses "Uncontrolled Recursion," and represents a failure to implement proper recursion limits and input validation in protocol parsing components. From an ATT&CK framework perspective, this vulnerability maps to techniques involving resource exhaustion and denial-of-service attacks, specifically targeting the availability aspect of the CIA triad. The attack surface extends beyond simple DNS servers to include any application that processes DNS messages through the affected crate, including web applications, network monitoring tools, and security appliances that rely on DNS resolution for their operations. Organizations should prioritize updating to version 0.5.0-alpha.3 or later, implementing network-level protections such as DNS message filtering, and conducting thorough testing to ensure that their applications are not vulnerable to this recursion-based attack vector. Additionally, implementing proper monitoring for unusual CPU usage patterns and recursive processing behaviors can help detect exploitation attempts before they cause significant disruption to services.