title: Mastodon vulnerable to Cross-site Scripting through oEmbed preview cards
description: Mastodon is a free, open-source social network server based on ActivityPub. Starting in version 1.3 and prior to versions 3.5.9, 4.0.5, and 4.1.3, an attacker using carefully crafted oEmbed data can bypass the HTML sanitization performed by Mastodon and include arbitrary HTML in oEmbed preview cards. This introduces a vector for cross-site scripting (XSS) payloads that can be rendered in the user's browser when a preview card for a malicious link is clicked through. Versions 3.5.9, 4.0.5, and 4.1.3 contain a patch for this issue.
problem types: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
affected:
{
vendor: mastodon
product: mastodon
versions:
version: >= 1.3, < 3.5.9, status: affected
version: >= 4.0.0, < 4.0.5, status: affected
version: >= 4.1.0, < 4.1.3, status: affected
}
metrics:
cvssV3_1: [
attackComplexity: LOW
attackVector: NETWORK
availabilityImpact: NONE
baseScore: 9.3
baseSeverity: CRITICAL
confidentialityImpact: HIGH
integrityImpact: HIGH
privilegesRequired: NONE
scope: CHANGED
userInteraction: REQUIRED
vectorString: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
version: 3.1
]