CVE-2019-12290 in Libidn2
Summary
by MITRE
GNU libidn2 before 2.2.0 fails to perform the roundtrip checks specified in RFC3490 Section 4.2 when converting A-labels to U-labels. This makes it possible in some circumstances for one domain to impersonate another. By creating a malicious domain that matches a target domain except for the inclusion of certain punycoded Unicode characters (that would be discarded when converted first to a Unicode label and then back to an ASCII label), arbitrary domains can be impersonated.
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Analysis
by VulDB Data Team • 01/17/2024
The vulnerability identified as CVE-2019-12290 resides within GNU libidn2 version 2.1.1 and earlier, representing a critical flaw in internationalized domain name handling that directly impacts DNS security and domain name spoofing capabilities. This issue stems from the library's failure to properly implement roundtrip validation as mandated by RFC3490 Section 4.2, which governs the conversion process between ASCII-compatible encoding (A-labels) and Unicode encoding (U-labels) for internationalized domain names. The flaw specifically manifests when the library processes domain names containing punycoded Unicode characters that, through the conversion process, can be manipulated to appear identical to legitimate domains while actually representing different hostnames.
The technical mechanism behind this vulnerability involves the improper handling of Unicode normalization and character encoding during domain name conversion processes. When a malicious actor crafts a domain name using specific Unicode characters that undergo normalization during the A-label to U-label conversion, followed by the reverse process back to A-label, the resulting domain appears visually identical to a legitimate target domain. This occurs because certain Unicode characters that are valid in the U-label format get discarded or normalized away during the roundtrip process, allowing attackers to create domains that look identical to legitimate ones but resolve to different IP addresses. The vulnerability operates at the intersection of internationalized domain name specifications and DNS security protocols, creating a pathway for domain name spoofing and potential man-in-the-middle attacks.
The operational impact of this vulnerability extends beyond simple domain impersonation, as it fundamentally undermines the security assumptions underlying DNS resolution and web browser trust models. Attackers can exploit this weakness to create malicious domains that appear legitimate to users, potentially enabling phishing attacks, credential theft, and unauthorized access to sensitive systems. The vulnerability affects any system relying on GNU libidn2 for internationalized domain name processing, including web browsers, email clients, and DNS resolution libraries that depend on this component for proper domain name handling. This creates a widespread risk across various networked applications and services that implement internationalized domain name support, particularly in environments where users may encounter domains with non-ASCII characters.
Mitigation strategies for CVE-2019-12290 primarily focus on upgrading to GNU libidn2 version 2.2.0 or later, which includes the proper implementation of RFC3490 Section 4.2 roundtrip validation requirements. System administrators should conduct comprehensive inventory checks to identify all systems utilizing affected versions of the library and prioritize patching efforts accordingly. Organizations should also implement additional monitoring mechanisms to detect suspicious domain name patterns and consider deploying DNS security extensions such as DNSSEC to provide additional layers of protection against domain impersonation attacks. The vulnerability aligns with CWE-184, which addresses incomplete implementation of security features, and maps to ATT&CK technique T1071.004 related to application layer protocol: DNS, highlighting the need for proper protocol implementation and validation in network security controls. Regular security audits and vulnerability assessments should include checks for proper internationalized domain name handling to prevent similar issues from arising in other components of the network infrastructure.