Denial of service via semicolon parameter bypass
Published Sep 25, 2025 · Updated Sep 25, 2025
Denial of service in Rack before 2.2.18 allows remote attackers to exhaust application memory through semicolon-separated query parameters. Rack::QueryParser#check_query_string counts only ampersands while the default separator splits on ampersands and semicolons, so semicolon-delimited fields evade params_limit. Exposure requires an application or middleware to call Rack::QueryParser directly without an explicit delimiter; typical Rack::Request handling is safe by default, while affected paths can consume excess CPU and memory until service is interrupted.
Summary
What happened
Denial of service in Rack before 2.2.18 allows remote attackers to exhaust application memory through semicolon-separated query parameters. Rack::QueryParser#check_query_string counts only ampersands while the default separator splits on ampersands and semicolons, so semicolon-delimited fields evade params_limit. Exposure requires an application or middleware to call Rack::QueryParser directly without an explicit delimiter; typical Rack::Request handling is safe by default, while affected paths can consume excess CPU and memory until service is interrupted.
The record
- CVE
- CVE-2025-59830
- Published
- Sep 25, 2025
- Updated
- Sep 25, 2025
- Vendor
- Rack
- Product
- Rack
- Classifications
- CWE-400, CWE-770, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 25, 2025CVE publishedPublication date reported by the CVE source.
- Sep 25, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 2.2.18
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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