Overview
CVE-2025-46727 is a significant cybersecurity vulnerability found in the Rack web server interface for Ruby. The flaw lies in the lack of an upper limit for the number of parameters parsed from query strings and form data, enabling malicious actors to trigger denial of service attacks. This vulnerability highlights the importance of robust cybersecurity practices and poses a critical risk to those utilizing older versions of Rack in their web applications.
Vulnerability Summary
CVE ID: CVE-2025-46727
Severity: High, CVSS Score: 7.5
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise and data leakage
Affected Products
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Product | Affected Versions
Rack | Prior to versions 2.2.14, 3.0.16, and 3.1.14
How the Exploit Works
The vulnerability lies in Rack’s QueryParser module, which parses query strings and form data into Ruby data structures without imposing any limit on the number of parameters. The QueryParser iterates over each `&`-separated key-value pair, adding it to a Hash with no upper bound on the total number of parameters. This allows an attacker to send a request containing an exceptionally large number of parameters, consuming excessive memory and CPU during parsing. This results in a denial of service as it can cause memory exhaustion or pin CPU resources, stalling or crashing the Rack server.
Conceptual Example Code
Below is a conceptual example of an HTTP request exploiting this vulnerability by sending a large number of parameters:
POST /vulnerable/endpoint HTTP/1.1
Host: target.example.com
Content-Type: application/x-www-form-urlencoded
param1=value1¶m2=value2¶m3=value3&...¶m1000000=value1000000In this example, the attacker sends a POST request with a million parameters in the request body, which would cause the server to consume excessive resources during parsing, potentially leading to a denial of service.
Mitigation
To mitigate the effects of this vulnerability, users should apply the vendor-provided patches (Rack versions 2.2.14, 3.0.16, and 3.1.14). In case patching is not immediately possible, one may use middleware to enforce a maximum query string size or parameter count, or employ a reverse proxy (such as Nginx) to limit request sizes and reject oversized query strings or bodies. Employing a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can also serve as a temporary mitigation measure. At the web server or CDN level, limiting request body sizes and query string lengths presents an effective mitigation strategy.
