CVE-2025-59830: Rack has an unsafe default in Rack :QueryParser Allows Params_limit Bypass Vulnerability

HIGH
Advisory Identifier: GHSA-625h-95r8-8xpm
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CVSS 7.5
CWE-400 CWE-770
Published
Advisory Summary

CVE-2025-59830 is a HIGH (CVSS 7.5) :queryparser allows params_limit bypass vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Rack has an unsafe default in Rack libraries in the RubyGems ecosystem. The issue involves :queryparser allows params_limit bypass via semicolon-separated parameters. Remediation is available by upgrading affected packages to version 2.2.18.

CVE-2025-59830 at a Glance

CVE Identifier CVE-2025-59830
GHSA Identifier GHSA-625h-95r8-8xpm
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product Rack has an unsafe default in Rack
Package Ecosystem RubyGems
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2025-59830

To remediate this vulnerability, upgrade all affected Rack has an unsafe default in Rack dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

rack fixed: 2.2.18 
Upgrade rack to 2.2.18
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for rack

How to Check if You Are Affected

To determine whether your application is affected by CVE-2025-59830, inspect your project dependencies for Rack has an unsafe default in Rack:

inspect dependencies for rack

Analyze the terminal output to locate any version of Rack has an unsafe default in Rack in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.2.18), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In Rack has an unsafe default in Rack, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

## Summary `Rack::QueryParser` in version `< 2.2.18` enforces its `params_limit` only for parameters separated by `&`, while still splitting on both `&` and `;`. As a result, attackers could use `;` separators to bypass the parameter count limit and submit more parameters than intended. ## Details The issue arises because `Rack::QueryParser#check_query_string` counts only `&` characters when determining the number of parameters, but the default separator regex `DEFAULT_SEP = /[&;] */n` splits on both `&` and `;`. This mismatch means that queries using `;` separators were not included in the parameter count, allowing `params_limit` to be bypassed. Other safeguards (`bytesize_limit` and `key_space_limit`) still applied, but did not prevent this particular bypass. ## Impact Applications or middleware that directly invoke `Rack::QueryParser` with its default configuration (no explicit delimiter) could be exposed to increased CPU and memory consumption. This can be abused as a limited denial-of-service vector. `Rack::Request`, the primary entry point for typical Rack applications, uses `QueryParser` in a safe way and does not appear vulnerable by default. As such, the severity is considered **low**, with the impact limited to edge cases where `QueryParser` is used directly. ## Mitigation * Upgrade to a patched version of Rack where both `&` and `;` are counted consistently toward `params_limit`. * If upgrading is not immediately possible, configure `QueryParser` with an explicit delimiter (e.g., `&`) to avoid the mismatch. * As a general precaution, enforce query string and request size limits at the web server or proxy layer (e.g., Nginx, Apache, or a CDN) to mitigate excessive parsing overhead.

CVE-2025-59830 Affected Rack has an unsafe default in Rack Versions

1 component(s)
Fixed Versions:
2.2.18
Product / Package Ecosystem Affected Versions Fixed Version
rack
gem/rack
RubyGems
< 2.2.18
2.2.18

References

GitHub Advisory / Wiki ADVISORY
https://github.com/rack/rack/security/advisories/GHSA-625h-95r8-8xpm
NVD — CVE-2025-59830 NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-59830
Security Fix Commit FIX COMMIT
https://github.com/rack/rack/commit/54e4ffdd5affebcb0c015cc6ae74635c0831ed71
Rack has an unsafe default in Rack Source Repository REPOSITORY
https://github.com/rack/rack

Frequently Asked Questions

What is CVE-2025-59830?
CVE-2025-59830 is a security vulnerability in Rack has an unsafe default in Rack involving :QueryParser allows params_limit bypass via semicolon-separated parameters under CWE-400: Uncontrolled Resource Consumption.
Which Rack has an unsafe default in Rack versions are affected?
Affected versions include releases prior to 2.2.18 across affected packages: rack.
What version fixes CVE-2025-59830?
Upgrading to 2.2.18 (or the latest patched release for your respective branch) resolves the vulnerability.
Is rack affected?
Yes, rack is affected in releases prior to 2.2.18. Upgrade your dependency to 2.2.18 or later.
What is the CVSS score of CVE-2025-59830?
CVE-2025-59830 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2025-59830?
CVE-2025-59830 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).
How can I check RubyGems dependencies for CVE-2025-59830?
Run the dependency tree command: 'inspect dependencies for rack'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-625h-95r8-8xpm",
  "modified" : "2025-09-25T16:39:27Z",
  "published" : "2025-09-25T16:39:27Z",
  "aliases" : [ "CVE-2025-59830" ],
  "summary" : "Rack has an unsafe default in Rack::QueryParser allows params_limit bypass via semicolon-separated parameters",
  "details" : "## Summary\n\n`Rack::QueryParser` in version `< 2.2.18` enforces its `params_limit` only for parameters separated by `&`, while still splitting on both `&` and `;`. As a result, attackers could use `;` separators to bypass the parameter count limit and submit more parameters than intended.\n\n## Details\n\nThe issue arises because `Rack::QueryParser#check_query_string` counts only `&` characters when determining the number of parameters, but the default separator regex `DEFAULT_SEP = /[&;] */n` splits on both `&` and `;`. This mismatch means that queries using `;` separators were not included in the parameter count, allowing `params_limit` to be bypassed.\n\nOther safeguards (`bytesize_limit` and `key_space_limit`) still applied, but did not prevent this particular bypass.\n\n## Impact\n\nApplications or middleware that directly invoke `Rack::QueryParser` with its default configuration (no explicit delimiter) could be exposed to increased CPU and memory consumption. This can be abused as a limited denial-of-service vector.\n\n`Rack::Request`, the primary entry point for typical Rack applications, uses `QueryParser` in a safe way and does not appear vulnerable by default. As such, the severity is considered **low**, with the impact limited to edge cases where `QueryParser` is used directly.\n\n## Mitigation\n\n* Upgrade to a patched version of Rack where both `&` and `;` are counted consistently toward `params_limit`.\n* If upgrading is not immediately possible, configure `QueryParser` with an explicit delimiter (e.g., `&`) to avoid the mismatch.\n* As a general precaution, enforce query string and request size limits at the web server or proxy layer (e.g., Nginx, Apache, or a CDN) to mitigate excessive parsing overhead.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "rack"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.2.18"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/rack/rack/security/advisories/GHSA-625h-95r8-8xpm"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-59830"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rack/rack/commit/54e4ffdd5affebcb0c015cc6ae74635c0831ed71"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/rack/rack"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-09-25T16:39:27Z",
    "nvd_published_at" : "2025-09-25T15:16:13Z"
  }
}