Misskey is an open source, federated social media platform. In affected versions missing validation in `ApRequestService.signedGet` and `HttpRequestService.getActivityJson` allows an attacker to create fake user profiles and forged notes. The spoofed users will appear to be from a different instance than the one where they actually exist, and the forged notes will appear to be posted by a different user. Vulnerable Misskey instances will accept the spoofed objects as valid, allowing an attacker to impersonate other users and instances. The attacker retains full control of the spoofed user / note and can interact like a real account. This issue has been addressed in version 2024.11.0-alpha.3. Users are advised to upgrade. There are no known workarounds for this vulnerability.
https://github.com/misskey-dev/misskey/security/advisories/GHSA-m2gq-69fp-6hv4
Published: 2024-12-18
Updated: 2025-11-26
Base Score: 8.5
Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:C/A:N
Severity: High
Base Score: 9.3
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:H/A:N
Severity: Critical
Base Score: 8.8
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:N/SC:L/SI:N/SA:L
Severity: High
EPSS: 0.00123