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computer vulnerability announce CVE-2017-5090

Chrome, Firefox: site spoofing via homographs

Synthesis of the vulnerability

An attacker can use a url with Unicode characters looking like ASCII characters, in order to deceive the victim.
Impacted products: Chrome, Firefox, SeaMonkey, Opera.
Severity of this bulletin: 2/4.
Consequences of an intrusion: data reading.
Hacker's origin: document.
Creation date: 18/04/2017.
Références of this threat: 1332714, CVE-2017-5090, VIGILANCE-VUL-22467.

Description of the vulnerability

Several Unicode characters (such as U+0430) look like the ASCII 'a' character. Some attackers use domain names containing these variants, in order to invite the victim to click on a link.

This type of attack, based on homographs, was already described in several bulletins (VIGILANCE-VUL-4729 and VIGILANCE-VUL-8497). Fixes are applied in most software.

However, when the name is only composed of Unicode characters, the Chrome and Firefox protections are bypassed. For example, https://xn--e1awd7f.com/ is displayed as https://www.epic.com/. Moreover, as a valid certificate for this domain can be obtained via Let's Encrypt, an attacker can easily spoof a TLS site.

An attacker can therefore use a url with Unicode characters looking like ASCII characters, in order to deceive the victim.
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