CVE-2025-46340 Misskey CSS Style Injection Vulnerability In `MkUrlPreview`
Attackers can inject CSS into URL previews to de-anonymize users or spoof UI elements, potentially leading to credential theft.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2025-46340?
CVE-2025-46340 is a high-severity cross-site scripting vulnerability in misskey-dev misskey, published on 5 May 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Which versions are affected by CVE-2025-46340?
It affects 1 product.
Products include Misskey Misskey.
How do I fix CVE-2025-46340?
No fix has been published for CVE-2025-46340 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2025-46340 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-46340 exists.
Other vulnerabilities in misskey-dev misskey
- CVE-2025-25306 Misskey's Incomplete Patch of CVE-2024-52591 Leads to Forgery of Federated Notes
- CVE-2023-49079 Misskey's missing signature validation allows arbitrary users to impersonate any remote user.
- CVE-2026-28431 Misskey lacks proper authorization checks and input validation
- CVE-2023-52139 Misskey vulnerable to improper authorization when accessing with third-party application
- CVE-2024-52590 Missing validation allows spoofed profiles in Misskey
Sources
Also known as GHSA-3p2w-xmv5-jm95.