The product displays information or identifiers to a user, but the display mechanism does not make it easy for the user to distinguish between visually similar or identical glyphs (homoglyphs), which may cause the user to misinterpret a glyph and perform an unintended, insecure action.

Some glyphs, pictures, or icons can be semantically distinct to a program, while appearing very similar or identical to a human user. These are referred to as homoglyphs. For example, the lowercase "l" (ell) and uppercase "I" (eye) have different character codes, but these characters can be displayed in exactly the same way to a user, depending on the font. This can also occur between different character sets. For example, the Latin capital letter "A" and the Greek capital letter "Α" (Alpha) are treated as distinct by programs, but may be displayed in exactly the same way to a user. Accent marks may also cause letters to appear very similar, such as the Latin capital letter grave mark "À" and its equivalent "Á" with the acute accent.

Adversaries can exploit this visual similarity for attacks such as phishing, e.g. by providing a link to an attacker-controlled hostname that looks like a hostname that the victim trusts. In a different use of homoglyphs, an adversary may create a back door username that is visually similar to the username of a regular user, which then makes it more difficult for a system administrator to detect the malicious username while reviewing logs.

Modes Of Introduction

Architecture and Design : This weakness may occur when characters from various character sets are allowed to be interchanged within a URL, username, email address, etc. without any notification to the user or underlying system being used.
Implementation

Applicable Platforms

Language

Class: Not Language-Specific (Undetermined)

Technologies

Class: Web Based (Sometimes)

Common Consequences

Observed Examples

Potential Mitigations

Phases : Implementation

Use a browser that displays Punycode for IDNs in the URL and status bars, or which color code various scripts in URLs.

Due to the prominence of homoglyph attacks, several browsers now help safeguard against this attack via the use of Punycode. For example, Mozilla Firefox and Google Chrome will display IDNs as Punycode if top-level domains do not restrict which characters can be used in domain names or if labels mix scripts for different languages.

Phases : Implementation

Use an email client that has strict filters and prevents messages that mix character sets to end up in a user's inbox.

Certain email clients such as Google's GMail prevent the use of non-Latin characters in email addresses or in links contained within emails. This helps prevent homoglyph attacks by flagging these emails and redirecting them to a user's spam folder.

Detection Methods

Manual Dynamic Analysis

If utilizing user accounts, attempt to submit a username that contains homoglyphs. Similarly, check to see if links containing homoglyphs can be sent via email, web browsers, or other mechanisms.
Effectiveness : Moderate

Vulnerability Mapping Notes

Rationale : This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comments : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Related Attack Patterns

References

REF-7

Writing Secure Code
Michael Howard, David LeBlanc.
https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223

REF-8

The 2011 IDN Homograph Attack Mitigation Survey
Gregory Baatard, Peter Hannay.
http://ro.ecu.edu.au/cgi/viewcontent.cgi?article=1174&context=ecuworks2012

Submission

Modifications