# 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. - **Severity:** High 7.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** No - **Published:** 5 May 2025 - **Updated:** 5 May 2025 - **Also known as:** GHSA-3p2w-xmv5-jm95 ## 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. Weakness: CWE-20 (Improper Input Validation), CWE-116 (Improper Encoding or Escaping of Output) ## Which versions are affected by CVE-2025-46340? It affects 1 product. Products: 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. ## 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](https://insights.sbomify.com/CVE-2025-25306/): Misskey's Incomplete Patch of CVE-2024-52591 Leads to Forgery of Federated Notes (critical 9.3) - [CVE-2023-49079](https://insights.sbomify.com/CVE-2023-49079/): Misskey's missing signature validation allows arbitrary users to impersonate any remote user. (critical 9.3) - [CVE-2026-28431](https://insights.sbomify.com/CVE-2026-28431/): Misskey lacks proper authorization checks and input validation (critical 9.2) - [CVE-2023-52139](https://insights.sbomify.com/CVE-2023-52139/): Misskey vulnerable to improper authorization when accessing with third-party application (critical 9.1) - [CVE-2024-52590](https://insights.sbomify.com/CVE-2024-52590/): Missing validation allows spoofed profiles in Misskey (high 8.8) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2025-46340 and fix it if it is affected. What it is: 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. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-46340 exists. Affected product: misskey-dev misskey. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2025-46340/ (Markdown: https://insights.sbomify.com/CVE-2025-46340/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2025-46340 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-46340 - OSV: https://osv.dev/vulnerability/CVE-2025-46340 --- From sbomify Insights: https://insights.sbomify.com/CVE-2025-46340/ Summaries are generated and may contain mistakes; the official description above is the record.