CVE-2025-27220
Ruby-Lang Cgi ≤ 0.3.5.1
Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:LSummary
CVE-2025-27220 is a medium-severity Inefficient Regular Expression Complexity (CWE-1333) vulnerability in Ruby-Lang Cgi. Its CVSS base score is 4.0 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Endpoint Denial of Service (T1499); ranked in the top 49% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2025-27220 is a Regular Expression Denial of Service (ReDoS) vulnerability in the Util#escapeElement method of the CGI gem for Ruby, affecting versions before 0.4.2. Published on 2025-03-04, it is classified under CWE-1333 and carries a CVSS v3.1 base score of 4.0 (AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L).
Remote attackers require no privileges or user interaction to exploit this over the network, though the attack demands high complexity. Exploitation triggers excessive resource consumption via malicious regular expression input, resulting in low-impact availability disruption with a changed scope.
Advisories recommend upgrading the CGI gem to version 0.4.2 or later for mitigation. Key references include the Ruby Advisory Database entry at https://github.com/rubysec/ruby-advisory-db/blob/master/gems/cgi/CVE-2025-27220.yml, a HackerOne disclosure report at https://hackerone.com/reports/2890322, and a Debian LTS announcement at https://lists.debian.org/debian-lts-announce/2025/03/msg00008.html.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-5509
Vulnerability Data
In the CGI gem before 0.4.2 for Ruby, a Regular Expression Denial of Service (ReDoS) vulnerability exists in the Util#escapeElement method.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation can discover inefficient regex patterns via performance or static analysis.
Development standards and tools can require safe regex construction and forbid known exponential patterns.
Denial-of-service protections limit resource exhaustion caused by expensive regex evaluation.
Input validation can constrain data that would otherwise trigger worst-case regex complexity.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing can detect and reject regex patterns with exponential worst-case complexity.
Secure development lifecycle mandates review of algorithmic efficiency, directly addressing ReDoS-prone regex.
Application security requirements can specify input-validation rules that limit regex complexity.
Secure architecture principles encourage avoidance of computationally expensive constructs such as catastrophic backtracking.
Secure coding standards explicitly prohibit or limit the use of inefficient regular expressions.