CVE-2023-27530
📋 TL;DR
This CVE describes a denial-of-service vulnerability in Rack's multipart MIME parsing code. Attackers can craft malicious requests that cause excessive processing time during multipart parsing, potentially leading to service unavailability. Affected systems are those running vulnerable versions of Rack (Ruby web server interface library) in applications that process multipart requests.
💻 Affected Systems
- Rack
- Ruby on Rails applications using Rack
- Any Ruby web application using Rack
📦 What is this software?
Rack by Rack
Rack by Rack
Rack by Rack
Rack by Rack
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to resource exhaustion, potentially affecting multiple applications on the same server if they share resources.
Likely Case
Degraded performance and intermittent service disruptions for applications processing multipart uploads.
If Mitigated
Minimal impact with proper request size limits, rate limiting, and updated Rack versions.
🎯 Exploit Status
The vulnerability requires crafting multipart requests with specific patterns that trigger inefficient parsing. No authentication is needed if the endpoint accepts multipart requests.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Rack >=3.0.4.2, >=2.2.6.3, >=2.1.4.3, >=2.0.9.3
Vendor Advisory: https://discuss.rubyonrails.org/t/cve-2023-27530-possible-dos-vulnerability-in-multipart-mime-parsing/82388
Restart Required: Yes
Instructions:
1. Update Rack gem: 'bundle update rack' or 'gem update rack'. 2. Verify the updated version with 'rack --version'. 3. Restart your Ruby application server (e.g., Puma, Unicorn, Passenger). 4. Test multipart request functionality.
🔧 Temporary Workarounds
Request size and rate limiting
allImplement limits on multipart request size and request rate to mitigate resource exhaustion.
# In Rails config/application.rb or middleware: Rack::Utils.multipart_part_limit = 128
# Configure web server (nginx example): client_max_body_size 10m;
# Use rate limiting middleware like rack-attack
Disable multipart parsing for non-essential endpoints
allRemove multipart support from endpoints that don't require file uploads or multipart forms.
# In Rails controller: skip_before_action :verify_authenticity_token, only: [:api_endpoint]
# Configure routes to reject multipart content types for specific endpoints
🧯 If You Can't Patch
- Implement strict request size limits and timeout configurations for multipart processing
- Deploy WAF rules to detect and block suspicious multipart request patterns
🔍 How to Verify
Check if Vulnerable:
Check Rack version with 'rack --version' or 'bundle show rack'. Compare against vulnerable versions: <3.0.4.2, <2.2.6.3, <2.1.4.3, <2.0.9.3.Check Version:
rack --versionVerify Fix Applied:
Confirm Rack version is >=3.0.4.2, >=2.2.6.3, >=2.1.4.3, or >=2.0.9.3. Test multipart request processing functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Unusually long processing times for multipart requests
- High CPU usage spikes during request processing
- Request timeouts on endpoints accepting file uploads
Network Indicators:
- Multiple large multipart requests from single sources
- Requests with unusual multipart boundary patterns
- Increased request size to upload endpoints
SIEM Query:
source="application.log" AND ("multipart" OR "upload") AND (duration>10s OR "timeout" OR "slow")🔗 References
- https://discuss.rubyonrails.org/t/cve-2023-27530-possible-dos-vulnerability-in-multipart-mime-parsing/82388
- https://lists.debian.org/debian-lts-announce/2023/04/msg00017.html
- https://security.netapp.com/advisory/ntap-20231208-0015/
- https://www.debian.org/security/2023/dsa-5530
- https://discuss.rubyonrails.org/t/cve-2023-27530-possible-dos-vulnerability-in-multipart-mime-parsing/82388
- https://lists.debian.org/debian-lts-announce/2023/04/msg00017.html
- https://security.netapp.com/advisory/ntap-20231208-0015/
- https://www.debian.org/security/2023/dsa-5530
