CVE-2017-7838 in Firefox
Summary
by MITRE
Punycode format text will be displayed for entire qualified international domain names in some instances when a sub-domain triggers the punycode display instead of the primary domain being displayed in native script and the sub-domain only displaying as punycode. This could be used for limited spoofing attacks due to user confusion. This vulnerability affects Firefox < 57.
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Analysis
by VulDB Data Team • 03/22/2023
The vulnerability described in CVE-2017-7838 represents a specific implementation flaw in Firefox's handling of internationalized domain names that can lead to user confusion and potential spoofing attacks. This issue occurs within the browser's display logic for punycode encoded domain names, which is a standard mechanism for representing non-ASCII characters in internet domain names using only ASCII characters. The problem manifests when a domain name contains both internationalized characters and subdomains, creating a scenario where the primary domain displays in its native script while subordinate domains are rendered using punycode encoding, resulting in inconsistent visual representation that can mislead users.
The technical flaw stems from Firefox's inconsistent handling of punycode display logic within qualified international domain names. When a domain contains international characters, the browser typically converts these to punycode format for technical processing while attempting to display them in native script for user readability. However, the vulnerability occurs when the subdomain level triggers punycode display while the main domain remains in native script format, creating a mixed visual representation. This inconsistency creates a situation where users may see part of a domain in their native language while other parts remain in the encoded format, potentially leading to confusion about the actual website being visited.
The operational impact of this vulnerability extends beyond simple visual inconsistency to potentially enable targeted spoofing attacks. Attackers could exploit this behavior by registering domain names that appear legitimate when viewed in their native script format but display suspicious punycode elements in subdomains. Users who are not familiar with the visual characteristics of punycode encoding may be misled into believing they are visiting a trusted website when in fact they are accessing a malicious domain. This vulnerability specifically affects Firefox versions prior to 57, making it a critical issue for users running older browser versions who remain exposed to potential deception attacks.
This vulnerability aligns with CWE-1004 which addresses insecure default conditions in web browsers, particularly concerning user interface elements that could be manipulated to cause confusion. The issue also relates to ATT&CK technique T1566 which involves social engineering through phishing attacks that exploit user trust in familiar interfaces. The inconsistency in domain name display creates an attack surface where users may not properly verify the authenticity of websites they trust, as the mixed display format can obscure malicious intent. Organizations should consider this vulnerability as part of their broader browser security management strategies, particularly when implementing security awareness training programs that address user recognition of potentially deceptive domain name presentations.
The mitigation for this vulnerability involves updating Firefox to version 57 or later, where the browser's domain name display logic has been improved to maintain consistent visual representation across all levels of internationalized domain names. Additionally, users should be educated about recognizing both native script and punycode representations of domain names, and organizations should consider implementing browser security policies that enforce automatic updates and regular security assessments. The fix implemented in Firefox 57 addresses the core display logic by ensuring that when any part of a domain name requires punycode encoding, the entire domain name is displayed consistently in punycode format, thereby eliminating the potential for user confusion and spoofing opportunities.