Misskey
CVE-2021-39195
MEDIUM
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V4 - API and Web Service URL allowlisting, SSRF prevention
MITRE ATT&CK
2 techniques across 2 tactics: Initial Access, Credential Access The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS score of 6.5 (MEDIUM). Attack characteristics: network attack vector, low complexity, low privileges required, no user interaction not required. |
| Exploit ScenarioDerived | A remote attacker could make the server perform requests to unintended internal or external resources by sending crafted requests to the affected application. |
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Alert meAnalysisAI
Misskey is an open source, decentralized microblogging platform. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. This Server-Side Request Forgery (SSRF) vulnerability could allow attackers to make the server perform requests to unintended internal or external resources.
RemediationAI
A vendor patch is available. Apply the latest security update as soon as possible. Validate and allowlist destination URLs, block requests to internal networks, use network segmentation.
Affects your stack
Find out whether the stacks and servers you run are on an affected version.
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This vulnerability is classified as Server-Side Request Forgery (SSRF) (CWE-918), which allows attackers to make the server perform requests to unintended internal or external resources. Misskey is an open source, decentralized microblogging platform. In affected versions a Server-Side Request Forgery vulnerability exists in "Upload from URL" and remote attachment handling. This could result in the disclosure of non-public information within the internal network. This has been fixed in 12.90.0. However, if you are using a proxy, you will need to take additional measures. As a workaround this exploit may be avoided by appropriately restricting access to private networks from the host where the application is running. Affected products include: Misskey.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionNVD
Misskey is an open source, decentralized microblogging platform. In affected versions a Server-Side Request Forgery vulnerability exists in "Upload from URL" and remote attachment handling. This could result in the disclosure of non-public information within the internal network. This has been fixed in 12.90.0. However, if you are using a proxy, you will need to take additional measures. As a workaround this exploit may be avoided by appropriately restricting access to private networks from the host where the application is running.
Threat Intelligence Overview
NVD
CVE.org
EPSS
GitHub
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Server-Side Request Forgery exploits applications that fetch remote resources based on user-supplied URLs.
Affected Products (CPE)NVD
Misskey is an open source, decentralized microblogging platform. Rated high severity (CVSS 7.5), this vulnerability is r
Missing authorization checks in Misskey's favorites and clips export feature allow any authenticated user to read the co
Login rate-limit bypass in Misskey (versions 2025.9.1 through 2025.11.x, and up to but not including 2025.12.0-alpha.2)
Misskey before 10.102.4 allows hijacking a user's token. Rated medium severity (CVSS 6.1), this vulnerability is remotel
Misskey is an open source, decentralized social media platform. Rated critical severity (CVSS 9.8), this vulnerability i
Misskey is an open source, decentralized social media platform. Rated critical severity (CVSS 9.6), this vulnerability i
Misskey is an open source, federated social media platform. Rated medium severity (CVSS 5.4), this vulnerability is remo
Signature validation bypass in Misskey (versions 12.37.0 through prior to 2026.5.4) allows an attacker to have spoofed A
JSON-LD signature validation in Misskey's ActivityPub federation layer accepts fraudulent federated activities due to a
Misskey is an open source, federated social media platform. Rated high severity (CVSS 8.8), this vulnerability is remote
Misskey is an open source, federated social media platform. Rated high severity (CVSS 8.8), this vulnerability is remote
Misskey is an open source, decentralized social media platform with ActivityPub support. Rated high severity (CVSS 8.8),
Exploit-DB