CVE-2025-46340: Misskey CSS Style Injection Vulnerability In `MkUrlPreview`
First published: Mon May 05 2025(Updated: )
Misskey is an open source, federated social media platform. Starting in version 12.0.0 and prior to version 2025.4.1, due to an oversight in the validation performed in `UrlPreviewService` and `MkUrlPreview`, it is possible for an attacker to inject arbitrary CSS into the `MkUrlPreview` component. `UrlPreviewService.wrap` falls back to returning the original URL if it's using a protocol that is likely to not be understood by Misskey, IE something other than `http` or `https`. This both can de-anonymize users and_allow further attacks in the client. Additionally, `MkUrlPreview` doesn't escape CSS when applying a `background-image` property, allowing an attacker to craft a URL that applies arbitrary styles to the preview element. Theoretically, an attacker can craft a CSS injection payload to create a fake error message that can deceive the user into giving away their credentials or similar sensitive information. Version 2025.4.1 contains a patch for the issue.
Credit: security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Misskey MkUrlPreview | >=12.0.0<2025.4.1 |
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Reference Links
Frequently Asked Questions
What is the severity of CVE-2025-46340?
CVE-2025-46340 is considered a high severity vulnerability due to its potential for allowing arbitrary CSS injection.
How do I fix CVE-2025-46340?
To fix CVE-2025-46340, upgrade to Misskey version 2025.4.1 or later as soon as possible.
What vulnerability does CVE-2025-46340 expose?
CVE-2025-46340 exposes the Misskey platform to potential cross-site injection attacks through arbitrary CSS.
Which versions of Misskey are affected by CVE-2025-46340?
CVE-2025-46340 affects Misskey versions from 12.0.0 up to but not including 2025.4.1.
What component is responsible for the vulnerability in CVE-2025-46340?
The vulnerability in CVE-2025-46340 is due to an oversight in the validation performed in the UrlPreviewService and MkUrlPreview components.
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