CVE-2023-27539
📋 TL;DR
CVE-2023-27539 is a denial-of-service vulnerability in Rack's header parsing component that allows attackers to cause excessive memory consumption by sending specially crafted HTTP headers. This affects any Ruby application using vulnerable versions of Rack, including Ruby on Rails applications. The vulnerability can lead to service unavailability.
💻 Affected Systems
- Rack
- Ruby on Rails
- Any Ruby application using Rack
📦 What is this software?
Rack by Rack
Rack by Rack
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to memory exhaustion, potentially affecting multiple applications on the same server.
Likely Case
Temporary service degradation or crashes requiring application restart.
If Mitigated
Minimal impact with proper rate limiting and request filtering in place.
🎯 Exploit Status
Exploitation requires sending specially crafted HTTP headers, which is straightforward for attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Rack 2.2.7 or 3.0.6
Vendor Advisory: https://github.com/advisories/GHSA-c6qg-cjj8-47qp
Restart Required: Yes
Instructions:
1. Update Gemfile to specify 'rack' gem version '>= 2.2.7' or '>= 3.0.6'. 2. Run 'bundle update rack'. 3. Restart your Ruby application server.
🔧 Temporary Workarounds
Rate limiting
allImplement rate limiting on HTTP requests to prevent mass exploitation attempts.
Web Application Firewall (WAF)
allConfigure WAF rules to block requests with suspicious or malformed headers.
🧯 If You Can't Patch
- Implement strict request size limits at the reverse proxy/load balancer level
- Monitor application memory usage and set up alerts for abnormal consumption patterns
🔍 How to Verify
Check if Vulnerable:
Check your Gemfile.lock or run 'bundle show rack' to see the installed Rack version.Check Version:
bundle show rack | grep -o 'rack.*'Verify Fix Applied:
Verify the Rack version is 2.2.7 or higher (for Rack 2.x) or 3.0.6 or higher (for Rack 3.x).📡 Detection & Monitoring
Log Indicators:
- Multiple requests with unusually large headers
- Application crashes or restarts with memory errors
- High memory consumption in application logs
Network Indicators:
- HTTP requests with abnormally large or malformed headers
- Sudden spikes in request volume from single IPs
SIEM Query:
source="application.logs" AND ("memory" OR "crash" OR "restart") AND "rack"🔗 References
- https://discuss.rubyonrails.org/t/cve-2023-27539-possible-denial-of-service-vulnerability-in-racks-header-parsing/82466
- https://github.com/advisories/GHSA-c6qg-cjj8-47qp
- https://github.com/rack/rack/commit/231ef369ad0b542575fb36c74fcfcfabcf6c530c
- https://github.com/rack/rack/commit/ee7919ea04303717858be1c3f16b406adc6d8cff
- https://lists.debian.org/debian-lts-announce/2023/04/msg00017.html
- https://security.netapp.com/advisory/ntap-20231208-0016/
- https://www.debian.org/security/2023/dsa-5530
