CVE-2022-42966 is a vulnerability classified under CWE-1333, which relates to inefficient regular expression complexity leading to a Regular Expression Denial of Service (ReDoS) attack. This vulnerability affects the 'cleo' package available on PyPI, specifically triggered when an attacker can supply arbitrary input to the Table.set_rows method. The core issue arises from the use of a regular expression within this method that exhibits exponential time complexity for certain crafted inputs. When exploited, this can cause the application to consume excessive CPU resources, leading to a denial of service condition. The vulnerability is remotely exploitable without requiring authentication or user interaction, but the attack complexity is rated high due to the need for crafting specific input patterns that trigger the inefficient regex. The CVSS v3.1 base score is 5.9 (medium severity), with the vector indicating network attack vector (AV:N), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), no impact on confidentiality or integrity (C:N/I:N), but high impact on availability (A:H). There are no known exploits in the wild, and no patches have been linked yet. The vulnerability was published on November 9, 2022, and is relevant to all versions of the cleo package (affectedVersions: 0, which likely means all versions up to the time of disclosure).

For European organizations, the primary impact of this vulnerability is the potential for denial of service attacks against applications or services that utilize the cleo package, especially those that invoke the Table.set_rows method with user-supplied input. Since cleo is a Python package often used for command-line interface utilities and scripting, organizations relying on automation, data processing, or internal tooling that includes this package could experience service disruptions. The denial of service could degrade operational availability, potentially affecting business continuity, especially in sectors where uptime is critical such as finance, healthcare, and public services. However, since the vulnerability does not affect confidentiality or integrity, the risk of data breaches or data manipulation is minimal. The high attack complexity somewhat limits widespread exploitation, but targeted attacks against critical infrastructure or high-value targets remain a concern. The lack of authentication requirement means that any exposed service or interface that processes untrusted input through cleo could be targeted remotely. Given the absence of known exploits in the wild, the immediate threat level is moderate, but organizations should not delay mitigation to prevent future exploitation.

Review and audit all internal and external applications, scripts, and services that use the cleo package, particularly those invoking Table.set_rows with user input. Implement input validation and sanitization to restrict or reject potentially malicious inputs that could trigger the vulnerable regular expression. Consider isolating or sandboxing components that use cleo to limit the impact of potential denial of service conditions on critical systems. Monitor resource utilization (CPU and memory) on systems running cleo-based applications to detect abnormal spikes indicative of ReDoS attempts. Where feasible, replace or upgrade the cleo package to a version that addresses this vulnerability once a patch is released; if no patch is available, consider alternative libraries or custom implementations that avoid vulnerable regex patterns. Apply rate limiting and network-level protections (e.g., Web Application Firewalls) to reduce the risk of automated or repeated exploitation attempts. Educate developers and DevOps teams about the risks of ReDoS vulnerabilities and encourage secure coding practices, especially when handling user input in regex operations.