CVE-2016-6261 in libidn
Summary
by MITRE
The idna_to_ascii_4i function in lib/idna.c in libidn before 1.33 allows context-dependent attackers to cause a denial of service (out-of-bounds read and crash) via 64 bytes of input.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability identified as CVE-2016-6261 affects the libidn library version 1.32 and earlier, specifically within the idna_to_ascii_4i function located in lib/idna.c. This flaw represents a critical security issue that enables context-dependent attackers to execute a denial of service attack through carefully crafted input sequences. The vulnerability manifests when the function processes 64 bytes of input data, leading to out-of-bounds memory read operations that ultimately cause application crashes and system instability. The issue stems from insufficient input validation and boundary checking within the internationalized domain name processing logic, which is fundamental to handling unicode domain names in internet protocols. Such vulnerabilities are particularly dangerous in network services and applications that process user-supplied domain name data, as they can be exploited to disrupt service availability and compromise system reliability.
The technical implementation of this vulnerability involves a specific memory access pattern where the idna_to_ascii_4i function fails to properly validate input boundaries during the processing of internationalized domain names. When an attacker provides exactly 64 bytes of input, the function's internal buffer management mechanisms become compromised, resulting in memory reads beyond allocated boundaries. This out-of-bounds read operation typically occurs during the transformation of unicode domain names into their ascii-compatible encoding format, a process essential for dns resolution and internet communication protocols. The flaw is classified under CWE-129 as an "Improper Validation of Array Index" and demonstrates how inadequate input sanitization can lead to memory corruption vulnerabilities. The vulnerability's exploitation requires minimal input size and can be executed remotely, making it particularly attractive to attackers seeking to disrupt services without requiring elevated privileges or complex attack vectors.
The operational impact of CVE-2016-6261 extends beyond simple service disruption to encompass broader security implications for systems relying on libidn for domain name processing. Applications that utilize this library for handling user input, web browsers, mail servers, and dns resolvers become vulnerable to crashes that can result in complete service unavailability. The vulnerability affects systems running affected versions of libidn, including various linux distributions, unix systems, and applications that incorporate this library into their networking stack. Network infrastructure components such as dns servers, proxy servers, and web applications that process domain names may experience cascading failures when exploited, potentially leading to extended downtime and service degradation. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1499.004 for Network Denial of Service, as it can be leveraged to create sustained disruption of network services through controlled input manipulation. The low complexity of exploitation combined with the high impact on service availability makes this vulnerability particularly dangerous in production environments.
Mitigation strategies for CVE-2016-6261 primarily focus on immediate remediation through library updates and system hardening measures. Organizations should prioritize upgrading to libidn version 1.33 or later, which contains the necessary patches to address the out-of-bounds read vulnerability. System administrators must conduct comprehensive vulnerability assessments to identify all systems utilizing affected libidn versions and implement patch management procedures to ensure timely deployment of security updates. Additional protective measures include implementing input validation at application layers, deploying network monitoring solutions to detect anomalous domain name processing patterns, and establishing robust application sandboxing to limit the impact of potential exploitation. The vulnerability also highlights the importance of proper software supply chain management and regular security auditing of third-party libraries. Organizations should consider implementing intrusion detection systems that can identify exploitation attempts targeting this specific vulnerability pattern and maintain detailed incident response procedures for handling denial of service attacks. Given the widespread use of libidn in internet infrastructure components, coordinated patch deployment across all affected systems remains critical to prevent exploitation and maintain service availability.