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+---
+gem: ruby_llm
+cve: 2026-67991
+ghsa: 42r3-x6vx-x49x
+url: https://nvd.nist.gov/vuln/detail/CVE-2026-67991
+title: Polynomial-Time Regular Expression Denial of Service (ReDoS) vulnerability
+date: 2026-08-13
+description: |
+  crmne/ruby_llm at commit fa6f279847d6d7027814539d9c0dfc3bbdfd2a83
+  contains a polynomial-time regular expression denial-of-service
+  condition in RubyLLM::Utils.underscore on Ruby 3.1.x.
+  A very long crafted class, agent, or tool name can cause
+  excessive CPU consumption and a denial of service.
+
+  Update: "the helper was extracted from existing code, so released
+  gems were affected too. All three reports concern polynomial-time
+  behavior on Ruby 3.1.x; exposure depends on untrusted data reaching
+  the affected operation."
+cvss_v3: 7.5
+unaffected_versions:
+  - "< 0.1.0.pre42"
+patched_versions:
+  - ">= 2.0.0.rc1"
+related:
+  url:
+    - https://nvd.nist.gov/vuln/detail/CVE-2026-67991
+    - https://github.com/crmne/ruby_llm/releases/tag/v2.0.0.rc1
+    - https://rubygems.org/gems/ruby_llm/versions/2.0.0.rc1
+    - https://github.com/crmne/ruby_llm/commit/9d75b033d7d00c4e1baa9b0afb4828faa8bd6602
+    - https://gist.github.com/Zykis1024/9f2d68fa3fd4e3a0ab83063bbe61a8e2
+    - https://github.com/crmne/ruby_llm/blob/fa6f279847d6d7027814539d9c0dfc3bbdfd2a83/lib/ruby_llm/utils.rb#L13
+    - https://github.com/advisories/GHSA-42r3-x6vx-x49x
+notes: |
+  - cvss_v3 from nvd.nist.gov and GHSA URL
+  - 9/14/2026: Versions data and "description" update came from developer email:
+    -- "CVE-2026-67991: affected >= 0.1.0.pre42, < 2.0.0.rc1.
+        Fix: https://github.com/crmne/ruby_llm/commit/9d75b033d7d00c4e1baa9b0afb4828faa8bd6602"