CVE-2021-4437 is a vulnerability identified in the dbartholomae lambda-middleware frameguard library, specifically affecting versions 1.0.0 through 1.0.4. The issue arises from inefficient regular expression complexity within the JSON Mime-Type Handler component, located in the file packages/json-deserializer/src/JsonDeserializer.ts. This inefficiency can be exploited by an attacker to cause excessive CPU consumption or denial of service conditions by crafting input that triggers worst-case behavior in the regular expression engine. The vulnerability is classified under CWE-1333, which relates to inefficient regular expression complexity leading to performance degradation. The vulnerability does not impact confidentiality or integrity but affects availability due to potential resource exhaustion. The vulnerability requires low privileges (PR:L), no user interaction (UI:N), and can be exploited remotely over a network (AV:A). The issue was addressed in version 1.1.0 of the library, with a patch identified by commit f689404d830cbc1edd6a1018d3334ff5f44dc6a6. There are no known exploits in the wild at this time, and the CVSS v3.1 base score is 3.5, indicating a low severity level. The vulnerability primarily impacts applications that use this middleware for JSON deserialization and frameguard functionality, potentially leading to denial of service through resource exhaustion when processing maliciously crafted JSON inputs.

For European organizations, the impact of CVE-2021-4437 is primarily related to availability disruptions. Organizations using the dbartholomae lambda-middleware frameguard library in their web applications or services may experience degraded performance or denial of service if attackers exploit the inefficient regular expression complexity. This could lead to service outages or degraded user experience, particularly in environments where the middleware processes untrusted JSON inputs. While the vulnerability does not compromise data confidentiality or integrity, availability issues can affect business continuity, especially for critical services relying on this middleware. The impact is more pronounced in high-availability environments or where the middleware is part of security controls (frameguard functionality) protecting against clickjacking or similar attacks. European organizations with web applications or APIs that incorporate this library should consider the risk of denial of service attacks that could disrupt operations or customer-facing services.

To mitigate this vulnerability, European organizations should upgrade the dbartholomae lambda-middleware frameguard library to version 1.1.0 or later, where the inefficient regular expression complexity issue has been resolved. Additionally, organizations should implement input validation and rate limiting on JSON inputs to reduce the risk of resource exhaustion attacks. Monitoring application performance and setting thresholds for CPU and memory usage can help detect exploitation attempts early. Employing Web Application Firewalls (WAFs) with rules to detect and block suspicious JSON payloads may also reduce exposure. Developers should review the use of regular expressions in JSON deserialization and consider alternatives or optimizations to avoid complex patterns that can be exploited. Finally, maintaining an up-to-date software inventory and applying patches promptly is critical to minimizing exposure.