CVE-2025-55735
📋 TL;DR
This stored cross-site scripting (XSS) vulnerability in flaskBlog allows attackers to inject malicious scripts into blog posts that execute when other users view those posts. All users of flaskBlog versions 2.8.0 and earlier are affected, particularly those who allow user-generated content.
💻 Affected Systems
- flaskBlog
📦 What is this software?
Flaskblog by Dogukanurker
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal session cookies, perform actions as authenticated users, deface the blog, or redirect users to malicious sites.
Likely Case
Attackers inject malicious JavaScript to steal user session cookies or credentials, potentially compromising user accounts.
If Mitigated
With proper input validation and output encoding, the malicious scripts would be rendered harmless as text rather than executed.
🎯 Exploit Status
Requires ability to create or edit posts; exploitation is straightforward once access is obtained
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.8.1 or later
Vendor Advisory: https://github.com/DogukanUrker/FlaskBlog/security/advisories/GHSA-gj9v-qhc3-gcfx
Restart Required: No
Instructions:
1. Update flaskBlog to version 2.8.1 or later
2. Replace '| safe' filter with proper output encoding in templates/routes.html
3. Ensure all user input is validated and sanitized
🔧 Temporary Workarounds
Remove unsafe filter
allRemove the '| safe' filter from the postContent rendering in templates/routes.html
Edit templates/routes.html and remove '| safe' filter from postContent variable
Implement input validation
allAdd server-side validation to sanitize post content before storage
Add HTML sanitization library (like bleach) and sanitize postContent before saving
🧯 If You Can't Patch
- Implement WAF rules to block XSS payloads in POST requests to create/edit endpoints
- Disable user-generated content functionality until patched
🔍 How to Verify
Check if Vulnerable:
Check if templates/routes.html uses '| safe' filter on postContent variable and version is ≤2.8.0Check Version:
Check flaskBlog version in package.json or setup.pyVerify Fix Applied:
Verify '| safe' filter is removed from templates/routes.html and version is ≥2.8.1📡 Detection & Monitoring
Log Indicators:
- Unusual post creation patterns
- Posts containing script tags or JavaScript code
Network Indicators:
- POST requests to create/edit endpoints with script tags or JavaScript
SIEM Query:
web_logs WHERE (method = 'POST' AND uri LIKE '%/post%') AND (body CONTAINS '<script>' OR body CONTAINS 'javascript:')