GHSA-625H-95R8-8XPM
Vulnerability from github – Published: 2025-09-25 16:39 – Updated: 2025-09-25 16:39Summary
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
∧are counted consistently towardparams_limit. - If upgrading is not immediately possible, configure
QueryParserwith 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.
{
"affected": [
{
"package": {
"ecosystem": "RubyGems",
"name": "rack"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.2.18"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2025-59830"
],
"database_specific": {
"cwe_ids": [
"CWE-400",
"CWE-770"
],
"github_reviewed": true,
"github_reviewed_at": "2025-09-25T16:39:27Z",
"nvd_published_at": "2025-09-25T15:16:13Z",
"severity": "HIGH"
},
"details": "## Summary\n\n`Rack::QueryParser` in version `\u003c 2.2.18` enforces its `params_limit` only for parameters separated by `\u0026`, while still splitting on both `\u0026` 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 `\u0026` characters when determining the number of parameters, but the default separator regex `DEFAULT_SEP = /[\u0026;] */n` splits on both `\u0026` 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 `\u0026` and `;` are counted consistently toward `params_limit`.\n* If upgrading is not immediately possible, configure `QueryParser` with an explicit delimiter (e.g., `\u0026`) 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.",
"id": "GHSA-625h-95r8-8xpm",
"modified": "2025-09-25T16:39:27Z",
"published": "2025-09-25T16:39:27Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
],
"summary": "Rack has an unsafe default in Rack::QueryParser allows params_limit bypass via semicolon-separated parameters"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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