Chat-processing delays via think-tag regex backtracking
Published Sep 29, 2026 · Updated Sep 29, 2026
Regular expression denial of service in RubyLLM think-tag parsing on Ruby 3.1.x allows attackers to delay chat completions via model responses. Two consecutive parsing expressions consume excessive CPU when a response contains many unterminated tags. Exploitation requires that such model output reach a consuming application's parser; the reported consequence is delayed processing, not data access or modification.
Summary
What happened
Regular expression denial of service in RubyLLM think-tag parsing on Ruby 3.1.x allows attackers to delay chat completions via model responses. Two consecutive parsing expressions consume excessive CPU when a response contains many unterminated tags. Exploitation requires that such model output reach a consuming application's parser; the reported consequence is delayed processing, not data access or modification.
The record
- CVE
- CVE-2026-67987
- Published
- Sep 29, 2026
- Updated
- Sep 29, 2026
- Vendor
- Carmine Paolino
- Product
- RubyLLM
- Classifications
- T1499.004
- Attack vector
- Unavailable
- Privileges
- Unavailable
Timeline
How it unfolded
- Sep 29, 2026CVE publishedPublication date reported by the CVE source.
- Sep 29, 2026Record updatedLatest update available in the CVE record.
Exploitability
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- Affected versionversion=n/a
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Activity data is delayed. The latest report is Sep 28, 2026.
Weakness, pattern, technique
Public exploit references
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Technologies
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