CVE-2023-42452 in Mastodon
Summary
by MITRE • 09/19/2023
Mastodon is a free, open-source social network server based on ActivityPub. In versions on the 4.x branch prior to versions 4.0.10, 4.2.8, and 4.2.0-rc2, under certain conditions, attackers can abuse the translation feature to bypass the server-side HTML sanitization, allowing unescaped HTML to execute in the browser. The impact is limited thanks to Mastodon's strict Content Security Policy, blocking inline scripts, etc. However a CSP bypass or loophole could be exploited to execute malicious XSS. Furthermore, it requires user interaction, as this can only occur upon clicking the “Translate” button on a malicious post. Versions 4.0.10, 4.2.8, and 4.2.0-rc2 contain a patch for this issue.
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Analysis
by VulDB Data Team • 10/13/2023
CVE-2023-42452 represents a cross-site scripting vulnerability within Mastodon's translation feature that affects versions prior to 4.0.10, 4.2.8, and 4.2.0-rc2. This vulnerability resides in the server-side HTML sanitization process that handles translated content, creating a potential attack vector where malicious actors can inject unescaped HTML into the translation functionality. The flaw specifically manifests when users interact with the "Translate" button on malicious posts, requiring user engagement to exploit the vulnerability. The technical implementation involves the translation feature failing to properly sanitize HTML content that gets rendered in the browser, potentially allowing attackers to inject malicious scripts despite the presence of Content Security Policy protections. This vulnerability falls under CWE-79 which specifically addresses Cross-Site Scripting flaws in software applications. The attack vector requires user interaction, making it a client-side exploitation scenario that aligns with ATT&CK technique T1203 for Exploitation for Client Execution, where attackers leverage user actions to trigger malicious code execution.
The security implications of this vulnerability are significant despite the presence of a strict Content Security Policy that blocks inline scripts and other common XSS attack vectors. The vulnerability demonstrates how HTML sanitization bypasses can occur even when robust security measures are in place, highlighting the complexity of modern web application security. The attack requires a specific user action - clicking the translate button on a malicious post - which limits the automatic exploitation potential but still presents a real risk to user safety. The vulnerability exists in the translation feature's handling of user-generated content, where translated HTML content is not properly escaped or filtered before being rendered in the browser context. This creates a scenario where an attacker could craft a malicious post containing HTML that appears legitimate but contains hidden script execution elements. The patch implemented in versions 4.0.10, 4.2.8, and 4.2.0-rc2 addresses this by strengthening the HTML sanitization process within the translation feature, ensuring that translated content undergoes proper escaping and filtering before being displayed to users.
The operational impact of CVE-2023-42452 extends beyond simple XSS execution as it represents a potential pathway for more sophisticated attacks that could leverage the translation feature as a foothold. While the current mitigation through CSP provides strong protection, the vulnerability demonstrates the importance of defense-in-depth strategies that do not rely solely on a single security control mechanism. The attack scenario requires social engineering to get users to click on malicious posts, making it less automated but still potentially dangerous in environments where users may be less security-aware. Security practitioners should understand that even when primary defenses like CSP are effective, secondary attack vectors through features like translation services can provide alternative paths to compromise. The vulnerability also highlights the challenges of maintaining security in open-source social platforms where user-generated content processing becomes a critical attack surface. Organizations running Mastodon instances should prioritize updating to patched versions immediately to prevent exploitation, as the vulnerability's requirement for user interaction does not eliminate the risk of successful attacks in targeted scenarios. The incident underscores the necessity of comprehensive input validation and output encoding across all application features, particularly those that process and display user-generated content in web interfaces.