CVE-2021-39195
📋 TL;DR
This CVE describes a Server-Side Request Forgery (SSRF) vulnerability in Misskey's 'Upload from URL' and remote attachment features. Attackers can exploit this to make the server send requests to internal network resources, potentially exposing sensitive information. All Misskey instances running affected versions are vulnerable.
💻 Affected Systems
- Misskey
📦 What is this software?
Misskey by Misskey
⚠️ Risk & Real-World Impact
Worst Case
Complete disclosure of internal network services, credentials, or sensitive data through SSRF to internal endpoints.
Likely Case
Information disclosure from internal services accessible to the Misskey server, potentially including metadata or configuration data.
If Mitigated
Limited or no impact if network segmentation prevents access to sensitive internal resources.
🎯 Exploit Status
SSRF vulnerabilities are commonly exploited and tooling exists for automated exploitation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 12.90.0
Vendor Advisory: https://github.com/misskey-dev/misskey/security/advisories/GHSA-mqv7-gxh4-r5vf
Restart Required: Yes
Instructions:
1. Backup your Misskey instance. 2. Update to version 12.90.0 or later using your package manager or manual update. 3. Restart the Misskey service. 4. If using a proxy, implement additional network restrictions as described in the advisory.
🔧 Temporary Workarounds
Network Segmentation
allRestrict the Misskey server's access to internal networks to prevent SSRF exploitation.
Use firewall rules to block outbound connections from Misskey to internal IP ranges (e.g., 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Misskey from internal resources
- Disable 'Upload from URL' and remote attachment features if not required
🔍 How to Verify
Check if Vulnerable:
Check your Misskey version - if it's below 12.90.0, you are vulnerable.Check Version:
Check the Misskey admin panel or configuration files for version informationVerify Fix Applied:
Confirm version is 12.90.0 or higher and test that SSRF attempts to internal addresses are blocked.📡 Detection & Monitoring
Log Indicators:
- Unusual outbound HTTP requests from Misskey to internal IP addresses
- Failed upload attempts with suspicious URLs
Network Indicators:
- HTTP requests from Misskey server to internal network segments
- Unusual traffic patterns from application server
SIEM Query:
source="misskey-logs" AND (url CONTAINS "10." OR url CONTAINS "172." OR url CONTAINS "192.168.")🔗 References
- https://github.com/misskey-dev/misskey/blob/develop/CHANGELOG.md#12900-20210904
- https://github.com/misskey-dev/misskey/commit/e1a8b158e04ad567d92d8daf3cc0898ee18f1a2e
- https://github.com/misskey-dev/misskey/security/advisories/GHSA-mqv7-gxh4-r5vf
- https://github.com/misskey-dev/misskey/blob/develop/CHANGELOG.md#12900-20210904
- https://github.com/misskey-dev/misskey/commit/e1a8b158e04ad567d92d8daf3cc0898ee18f1a2e
- https://github.com/misskey-dev/misskey/security/advisories/GHSA-mqv7-gxh4-r5vf
