CVE-2021-39169 XSS vulnerability using dialog

What is CVE-2021-39169?

CVE-2021-39169 is a high-severity cross-site scripting vulnerability in misskey-dev misskey, published on 27 Aug 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

Official description

Misskey is a decentralized microblogging platform. In versions of Misskey prior to 12.51.0, malicious actors can use the web client built-in dialog to display a malicious string, leading to cross-site scripting (XSS). XSS could compromise the API request token. This issue has been fixed in version 12.51.0. There are no known workarounds aside from upgrading.

Weakness: CWE-79

Which versions are affected by CVE-2021-39169?

It affects 1 product.

Products include Misskey Misskey.

How do I fix CVE-2021-39169?

No fix has been published for CVE-2021-39169 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-2021-39169 being exploited?

There is no known exploitation of CVE-2021-39169 in the wild and no public exploit code.

Other vulnerabilities in misskey-dev misskey

• CVE-2025-25306 Misskey's Incomplete Patch of CVE-2024-52591 Leads to Forgery of Federated Notes Critical 9.3
• CVE-2023-49079 Misskey's missing signature validation allows arbitrary users to impersonate any remote user. Critical 9.3
• CVE-2026-28431 Misskey lacks proper authorization checks and input validation Critical 9.2
• CVE-2023-52139 Misskey vulnerable to improper authorization when accessing with third-party application Critical 9.1
• CVE-2024-52590 Missing validation allows spoofed profiles in Misskey High 8.8

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-pmmv-jwqh-f5ww.