CVE-2019-18224 in Libidn2
Summary
by MITRE
idn2_to_ascii_4i in lib/lookup.c in GNU libidn2 before 2.1.1 has a heap-based buffer overflow via a long domain string.
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Analysis
by VulDB Data Team • 01/17/2024
The vulnerability CVE-2019-18224 represents a critical heap-based buffer overflow in the GNU libidn2 library, specifically within the idn2_to_ascii_4i function located in lib/lookup.c. This flaw affects versions prior to 2.1.1 and stems from inadequate input validation when processing internationalized domain names. The vulnerability manifests when the library encounters excessively long domain strings that exceed the allocated buffer boundaries during the conversion process from internationalized domain names to ASCII format. The buffer overflow occurs because the implementation fails to properly check string length limits before performing memory operations, creating an exploitable condition that can lead to arbitrary code execution or system instability. This vulnerability is particularly concerning as it resides in a widely used library that handles domain name processing across numerous applications and systems that rely on internationalized domain name support.
The technical implementation of this vulnerability involves the idn2_to_ascii_4i function which processes domain names containing international characters and converts them to ASCII representation for compatibility with DNS systems. When a domain string exceeds the predetermined buffer size limits, the function continues to write data beyond the allocated memory boundaries, causing adjacent memory locations to be overwritten. This heap-based overflow can be exploited by attackers who craft maliciously long domain names that trigger the vulnerable code path. The flaw directly maps to CWE-121, which describes heap-based buffer overflow conditions where insufficient bounds checking allows data to be written beyond allocated heap memory regions. The vulnerability demonstrates poor memory management practices and inadequate input sanitization that violates fundamental security principles for buffer handling in C-based applications.
The operational impact of CVE-2019-18224 extends beyond simple denial of service scenarios to potentially enable remote code execution in vulnerable environments. Systems that utilize GNU libidn2 for domain name processing, including web servers, email systems, and network applications, become susceptible to exploitation when processing untrusted domain inputs. Attackers can leverage this vulnerability to execute arbitrary code on affected systems, potentially leading to complete system compromise or privilege escalation. The vulnerability affects a broad ecosystem since GNU libidn2 is integrated into numerous software packages and operating systems that handle internationalized domain names. This includes web browsers, mail clients, DNS servers, and various network infrastructure components that depend on proper international domain name handling. The exploitability of this vulnerability is heightened in environments where applications do not properly validate or sanitize domain name inputs before passing them to the vulnerable library functions.
Mitigation strategies for CVE-2019-18224 primarily focus on upgrading to GNU libidn2 version 2.1.1 or later, which contains the necessary patches to address the buffer overflow condition. System administrators should prioritize updating all affected systems and applications that rely on this library, particularly those handling untrusted domain name inputs. Additional protective measures include implementing input validation at application layers to reject excessively long domain strings before they reach the vulnerable library functions, employing address space layout randomization to complicate exploitation attempts, and utilizing heap protection mechanisms such as stack canaries. Organizations should also consider implementing network monitoring to detect potential exploitation attempts involving malformed domain names. The vulnerability highlights the importance of regular security updates and proper input validation practices, aligning with ATT&CK technique T1059.007 for command and scripting interpreter usage, where attackers may leverage such vulnerabilities to execute malicious payloads. Security teams should conduct comprehensive vulnerability assessments to identify all systems using affected versions of the library and establish monitoring procedures to detect potential exploitation attempts through abnormal domain name processing patterns.