Overview
This report covers a significant vulnerability found in Rack, a modular Ruby web server interface. The flaw, identified as CVE-2025-59830, is a parameter count limit bypass vulnerability that may lead to increased CPU and memory consumption, potentially causing a denial of service. This vulnerability is of importance to all businesses and individuals using affected versions of Rack, as it poses a risk to system stability and data security.
Vulnerability Summary
CVE ID: CVE-2025-59830
Severity: High (CVSS: 7.5)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage due to increased CPU and memory consumption
Affected Products
Product | Affected Versions
Rack | Prior to 2.2.18
How the Exploit Works
The vulnerability lies in the Rack::QueryParser module which enforces its params_limit only for parameters separated by &, while it should also split on ;. This allows attackers to bypass the parameter count limit by using ; separators to submit more parameters than intended. The impact is increased CPU and memory usage, which can be leveraged for a denial-of-service attack.
Conceptual Example Code
The following is a conceptual example of how the vulnerability might be exploited. This example uses a hypothetical HTTP request with a payload that abuses the parameter count bypass vulnerability.
POST /vulnerable/endpoint HTTP/1.1
Host: target.example.com
Content-Type: application/x-www-form-urlencoded
param1=value1¶m2=value2;param3=value3;param4=value4;param5=value5;...;paramN=valueN
In the above example, the attacker is sending a POST request with more parameters than the server is designed to handle, using the ; character to bypass the parameter count limit.
Mitigation
It is recommended to apply the vendor patch as soon as possible. If immediate patching is not possible, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can serve as temporary mitigation. The vulnerability has been patched in Rack version 2.2.18.
