What is CVE-2025-46340?

CVE-2025-46340 is a high-severity vulnerability in Misskey, classified under Improper Input Validation. CVSS score: 7.2/10. Published 2025-05-05.

How severe is CVE-2025-46340?

High severity. CVSS v3 base score is 7.2 out of 10.

Is CVE-2025-46340 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Improper input validation in Misskey

CVE-2025-46340

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.

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published 2025-05-05 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.002 (14.0th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 14.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000

Affected products

Misskey
Misskey-Dev Misskey — versions >= 12.0.0, < 2025.4.1

Weakness classification (CWE)

Public proof-of-concept exploits

fkie-cad/nvd-json-data-feeds

References

github.com/misskey-dev/misskey/security/advisories/GHSA-3p2w-xmv5-jm95 (Vendor Advisory)
github.com/misskey-dev/misskey/commit/d10fdfe9738b17a9d81037c031b40a2cc4cb8038 (Patch)

Frequently asked questions

What is CVE-2025-46340?: CVE-2025-46340 is a high-severity vulnerability in Misskey, classified under Improper Input Validation. CVSS score: 7.2/10. Published 2025-05-05.
How severe is CVE-2025-46340?: High severity. CVSS v3 base score is 7.2 out of 10.
Is CVE-2025-46340 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.