CVE-2020-5243 in UAP-Core
Summary
by MITRE
uap-core before 0.7.3 is vulnerable to a denial of service attack when processing crafted User-Agent strings. Some regexes are vulnerable to regular expression denial of service (REDoS) due to overlapping capture groups. This allows remote attackers to overload a server by setting the User-Agent header in an HTTP(S) request to maliciously crafted long strings. This has been patched in uap-core 0.7.3.
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Analysis
by VulDB Data Team • 04/02/2024
The vulnerability identified as CVE-2020-5243 affects the uap-core library version 0.7.2 and earlier, representing a critical security flaw that exposes systems to denial of service attacks through manipulation of User-Agent headers. This library is commonly used for parsing and identifying user agents in web applications, making it a potential attack vector for adversaries seeking to disrupt service availability. The vulnerability stems from the library's handling of regular expressions within its User-Agent string processing functionality, where specific regex patterns contain overlapping capture groups that create opportunities for malicious input to cause excessive computational overhead.
The technical flaw manifests through regular expression denial of service attacks, a well-documented vulnerability category classified under CWE-400 in the Common Weakness Enumeration framework. The vulnerable regex patterns in uap-core contain overlapping capture groups that allow attackers to craft User-Agent strings that cause the regular expression engine to perform exponential backtracking when processing these inputs. This occurs because the overlapping patterns create multiple possible matches that the engine must explore, leading to a dramatic increase in processing time as input length grows. When an attacker sends a carefully constructed long User-Agent string, the server's processing time increases exponentially rather than linearly, consuming significant computational resources and potentially leading to complete service unavailability.
The operational impact of this vulnerability extends beyond simple service disruption, as it represents a sophisticated attack vector that can be exploited remotely without requiring authentication or special privileges. Attackers can leverage this weakness by simply sending HTTP requests with maliciously crafted User-Agent headers, making the attack surface extremely broad across any web application or service that utilizes the vulnerable uap-core library. The vulnerability affects any system that processes HTTP requests and relies on user agent parsing for functionality such as analytics, security monitoring, or access control decisions. This makes it particularly dangerous in environments where user agent data is processed for security purposes, as the attack could potentially bypass security measures while simultaneously consuming system resources.
Mitigation strategies for CVE-2020-5243 focus primarily on upgrading to uap-core version 0.7.3 or later, which contains the necessary patches to address the regex vulnerability. Organizations should conduct thorough inventory assessments to identify all systems utilizing the vulnerable library and prioritize patching efforts accordingly. Additional defensive measures include implementing rate limiting on User-Agent header processing, setting maximum length constraints on incoming User-Agent strings, and deploying web application firewalls that can detect and block suspicious patterns in HTTP headers. The ATT&CK framework categorizes this type of vulnerability under T1499.004 for Network Denial of Service, highlighting the importance of implementing proper input validation and resource management controls. System administrators should also consider monitoring for unusual processing patterns or resource consumption spikes that might indicate exploitation attempts, as these could serve as early warning indicators of active attacks against the vulnerable components.