Vulnerability · Published May 5, 2025 · Assigned by GitHub_M
CVE-2025-46340Misskey CSS Style Injection Vulnerability In `MkUrlPreview`
High 7.2
In plain English
A high-severity improper input validation in misskey from misskey-dev. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities).
Official description
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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| misskey-dev | misskey | >= 12.0.0, < 2025.4.1 |
Weakness: CWE-20, CWE-116 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N