CVE-2021-3819
📋 TL;DR
CVE-2021-3819 is a Cross-Site Request Forgery (CSRF) vulnerability in firefly-iii personal finance software. It allows attackers to trick authenticated users into performing unintended actions like modifying financial data. All firefly-iii users with web access are affected.
💻 Affected Systems
- firefly-iii
📦 What is this software?
Firefly Iii by Firefly Iii
⚠️ Risk & Real-World Impact
Worst Case
Attackers could manipulate financial transactions, delete accounts, or modify user settings without the victim's knowledge, potentially leading to financial loss or data corruption.
Likely Case
Attackers could create unauthorized transactions, modify existing records, or change account settings through crafted malicious web pages.
If Mitigated
With proper CSRF protections, requests would require valid tokens, preventing unauthorized actions even if users visit malicious sites.
🎯 Exploit Status
CSRF attacks are well-understood and easy to implement; exploitation requires the victim to be authenticated and visit a malicious page.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Commit 578f350498b75f31d321c78a608c7f7b3b7b07e9 or later
Vendor Advisory: https://github.com/firefly-iii/firefly-iii/commit/578f350498b75f31d321c78a608c7f7b3b7b07e9
Restart Required: Yes
Instructions:
1. Update firefly-iii to the latest version. 2. Apply commit 578f350498b75f31d321c78a608c7f7b3b7b07e9 if using source. 3. Restart the web server.
🔧 Temporary Workarounds
Enable CSRF Protection
allEnsure CSRF tokens are properly implemented in all forms and validated server-side.
Use SameSite Cookies
allConfigure session cookies with SameSite=Strict or Lax to limit cross-site requests.
Set-Cookie: session=value; SameSite=Strict; Secure; HttpOnly
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to detect and block CSRF attempts.
- Educate users about the risks of clicking unknown links while authenticated.
🔍 How to Verify
Check if Vulnerable:
Check if firefly-iii version is before commit 578f350498b75f31d321c78a608c7f7b3b7b07e9 by reviewing the source code or version history.Check Version:
Check the firefly-iii version in the web interface or via the application's version file.Verify Fix Applied:
Verify that CSRF tokens are present in all forms and validated on the server by inspecting network requests.📡 Detection & Monitoring
Log Indicators:
- Multiple failed form submissions without CSRF tokens
- Unusual transaction patterns from same IP
Network Indicators:
- HTTP POST requests without Referer headers or CSRF tokens
- Requests from unexpected origins
SIEM Query:
source="firefly-iii" AND (event="form_submission_failed" OR event="transaction_created") AND csrf_token="missing"🔗 References
- https://github.com/firefly-iii/firefly-iii/commit/578f350498b75f31d321c78a608c7f7b3b7b07e9
- https://huntr.dev/bounties/da82f7b6-4ffc-4109-87a4-a2a790bd44e5
- https://github.com/firefly-iii/firefly-iii/commit/578f350498b75f31d321c78a608c7f7b3b7b07e9
- https://huntr.dev/bounties/da82f7b6-4ffc-4109-87a4-a2a790bd44e5
