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.
CWE-1007 Base Incomplete
Insufficient Visual Distinction of Homoglyphs Presented to User
This vulnerability occurs when an application shows text or symbols to users without clearly distinguishing between characters that look identical or very similar (called homoglyphs). Because users…
Definition
What is CWE-1007?
This vulnerability occurs when an application shows text or symbols to users without clearly distinguishing between characters that look identical or very similar (called homoglyphs). Because users can't easily tell these characters apart, they might misinterpret information and accidentally perform unsafe actions, like clicking a malicious link.
Homoglyphs are different characters that appear identical or nearly identical on screen. For example, a lowercase 'L' and an uppercase 'i' can look the same in many fonts, and the Latin 'A' is visually identical to the Greek 'Alpha'. While software treats these as completely different characters, users can't see the difference, creating a gap between what the system understands and what the user perceives.
Attackers exploit this visual ambiguity to trick users. A common method is creating deceptive phishing links or hostnames that mimic trusted sites. Similarly, an attacker might register a username like 'Admin' (with a Cyrillic 'A') that looks identical to the real 'Admin' account, making malicious activity harder to spot in system logs. This highlights a critical need for interfaces to help users visually distinguish between potentially confusing characters.
Real-world impact
Real-world CVEs caused by CWE-1007
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web forum allows impersonation of users with homoglyphs in account names
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Improper character restriction in URLs in web browser
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Incomplete denylist does not include homoglyphs of "/" and "?" characters in URLs
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web browser does not convert hyphens to punycode, allowing IDN spoofing in URLs
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homoglyph spoofing using punycode in URLs and certificates
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homoglyph spoofing using punycode in URLs and certificates
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homoglyph spoofing using punycode in URLs and certificates
How attackers exploit it
Step-by-step attacker path
- 1
The following looks like a simple, trusted URL that a user may frequently access.
- 2
However, the URL above is comprised of Cyrillic characters that look identical to the expected ASCII characters. This results in most users not being able to distinguish between the two and assuming that the above URL is trusted and safe. The "e" is actually the "CYRILLIC SMALL LETTER IE" which is represented in HTML as the character е, while the "a" is actually the "CYRILLIC SMALL LETTER A" which is represented in HTML as the character а. The "p", "c", and "o" are also Cyrillic characters in this example. Viewing the source reveals a URL of "http://www.еxаmрlе.соm". An adversary can utilize this approach to perform an attack such as a phishing attack in order to drive traffic to a malicious website.
- 3
The following displays an example of how creating usernames containing homoglyphs can lead to log forgery.
- 4
Assume an adversary visits a legitimate, trusted domain and creates an account named "admin", except the 'a' and 'i' characters are Cyrillic characters instead of the expected ASCII. Any actions the adversary performs will be saved to the log file and look like they came from a legitimate administrator account.
- 5
Upon closer inspection, the account that generated three of these log entries is "аdmіn". Only the third log entry is by the legitimate admin account. This makes it more difficult to determine which actions were performed by the adversary and which actions were executed by the legitimate "admin" account.
Vulnerable code example
Vulnerable code
The following looks like a simple, trusted URL that a user may frequently access.
http://www.еxаmрlе.соm Attacker payload
The following looks like a simple, trusted URL that a user may frequently access.
http://www.еxаmрlе.соm Secure code example
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-1007
- 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.
- 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 signals
How to detect CWE-1007
CWE-1007
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Frequently asked questions What is CWE-1007?
How serious is CWE-1007?
What languages or platforms are affected by CWE-1007?
How can I prevent CWE-1007?
How does Plexicus detect and fix CWE-1007?
Where can I learn more about CWE-1007?
Frequently asked questions
What is CWE-1007?
This vulnerability occurs when an application shows text or symbols to users without clearly distinguishing between characters that look identical or very similar (called homoglyphs). Because users can't easily tell these characters apart, they might misinterpret information and accidentally perform unsafe actions, like clicking a malicious link.
How serious is CWE-1007?
MITRE rates the likelihood of exploit as Medium — exploitation is realistic but typically requires specific conditions.
What languages or platforms are affected by CWE-1007?
MITRE lists the following affected platforms: Web Based.
How can I prevent CWE-1007?
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. Use an email client that has strict filters…
How does Plexicus detect and fix CWE-1007?
Plexicus's SAST engine matches the data-flow signature for CWE-1007 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-1007?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1007.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-1007
CWE-451 Parent
User Interface (UI) Misrepresentation of Critical Information
This vulnerability occurs when a user interface fails to accurately display or highlight crucial information, potentially misleading users…
CWE-1021 Sibling
Improper Restriction of Rendered UI Layers or Frames
This vulnerability occurs when a web application fails to properly control whether its pages can be embedded within frames or UI layers…
Resources
Further reading
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