Service interruption via polynomial underscore regular expression
Published Aug 13, 2026 · Updated Aug 13, 2026
Regular expression denial of service in RubyLLM at the cited commit allows attackers to exhaust CPU through crafted class, agent, or tool names. The second gsub in RubyLLM::Utils.underscore applies /([a-z\d])([A-Z])/ to an unbounded name, exhibiting polynomial processing time on Ruby 3.1.x. An application must pass an attacker-controlled, very long class, agent, or tool name to this helper; successful input monopolizes CPU and interrupts service.
Summary
What happened
Regular expression denial of service in RubyLLM at the cited commit allows attackers to exhaust CPU through crafted class, agent, or tool names. The second gsub in RubyLLM::Utils.underscore applies /([a-z\d])([A-Z])/ to an unbounded name, exhibiting polynomial processing time on Ruby 3.1.x. An application must pass an attacker-controlled, very long class, agent, or tool name to this helper; successful input monopolizes CPU and interrupts service.
The record
- CVE
- CVE-2026-67991
- Published
- Aug 13, 2026
- Updated
- Aug 13, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-1333, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 13, 2026CVE publishedPublication date reported by the CVE source.
- Aug 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
What conditions does exploitation require?
What is affected?
Affected products and versions are unavailable in this record.
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo