CVE-2021-33503 is a high-severity vulnerability found in the urllib3 library versions before 1.26.5. This vulnerability allows attackers to exploit a flaw in the authority regular expression used to parse URLs. Specifically, when provided with a URL that contains many '@' characters in the authority component, the parsing mechanism can experience catastrophic backtracking, leading to a denial of service (DoS) condition. The impact of this vulnerability is significant as it can disrupt the availability of applications relying on the urllib3 library.
The severity of this vulnerability is classified as high, with a CVSS score of 7.5. This score indicates a network attack vector with low complexity and no required privileges or user interaction. The primary risk to organizations includes potential downtime and service disruptions, making it imperative for affected entities to act swiftly.
Currently, there are no known exploits for this vulnerability, but organizations should remain vigilant. The urgency for defenders is high as the impact on availability is rated as high, necessitating immediate attention to patching and remediation efforts.
Organizations should prioritize patching immediately.
Vulnerability Details
The official description of CVE-2021-33503 states: 'An issue was discovered in urllib3 before 1.26.5. When provided with a URL containing many @ characters in the authority component, the authority regular expression exhibits catastrophic backtracking, causing a denial of service if a URL were passed as a parameter or redirected to via an HTTP redirect.' This vulnerability falls under the Common Weakness Enumeration (CWE) classification of CWE-400, which refers to 'Uncontrolled Resource Consumption.'
The CVSS score of 7.5 reflects its high severity, indicating the potential for a severe impact on availability. The vulnerability affects a range of products, including urllib3, Fedora (versions 33 and 34), and various Oracle components such as the enterprise manager ops center and instantis enterprisetrack.
Technical Analysis
The root cause of CVE-2021-33503 lies in the design of the authority parsing mechanism in urllib3. URLs that contain numerous '@' characters can trigger a catastrophic backtracking situation in the regular expression engine, which results in excessive resource consumption. This condition can lead to a denial of service as the parsing operation takes an inordinate amount of time or fails entirely.
The attack vector is network-based, meaning that an attacker can exploit this vulnerability remotely without needing physical access to the affected system. The complexity of the attack is low, allowing even less sophisticated attackers to achieve a denial of service by carefully crafting URLs. Importantly, the exploitation of this vulnerability does not require any privileges or user interaction, making it particularly dangerous.
Regarding the impacts of exploitation, the confidentiality and integrity of the system are not affected; however, the availability impact is rated as high. This means that while sensitive data remains secure, the service may become unavailable, leading to significant operational disruptions.
Risk & Impact Analysis
The real-world risk associated with CVE-2021-33503 is that organizations using affected versions of urllib3 may experience denial of service during normal operations. This vulnerability can be exploited by attackers who can craft URLs with multiple '@' characters, effectively overwhelming the service and disrupting availability. The blast radius could encompass any application utilizing urllib3 for HTTP requests, resulting in widespread service outages.
Given the CVSS score of 7.5 and the absence of confirmed public exploits, organizations should assess their exposure to this vulnerability and prioritize patching in their maintenance cycles. The urgency for remediation is high, as this vulnerability could lead to significant downtime and impact operational capabilities.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
CVE-2021-33503 affects urllib3 versions before 1.26.5. Additionally, it impacts Fedora versions 33 and 34, and various Oracle components, including the enterprise manager ops center and instantis enterprisetrack. Organizations should ensure they are running updated versions to mitigate this vulnerability.
Mitigation & Remediation
To mitigate the risks associated with CVE-2021-33503, organizations must apply the appropriate patches to update urllib3 to version 1.26.5 or later. This patch addresses the catastrophic backtracking issue in the authority regular expression. In cases where immediate patching is not feasible, organizations should implement network controls to restrict access to potentially malicious URLs and monitor for any unusual behavior.
For organizations that require assistance in validating the effectiveness of their remediation efforts, penetration testing can provide valuable insights. Engaging in penetration testing can help identify any remaining vulnerabilities in the system.
Detection Guidance
Organizations should monitor logs for indicators related to unusual URL patterns that include excessive '@' characters. Behavioral anomalies in application performance, particularly during URL parsing operations, should also be investigated. Network signatures that indicate exploitation attempts should be established to enhance detection capabilities.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2021-33503 lies in its potential to disrupt services reliant on urllib3 for HTTP requests. This vulnerability represents a noteworthy trend in denial of service attacks that leverage common patterns in URL handling. Security teams should learn from this incident to strengthen their defenses against similar vulnerabilities in the future.
Adopting proactive measures, such as conducting regular assessments and integrating security into the development lifecycle, can significantly reduce the risk of similar vulnerabilities. For further guidance on securing applications, organizations may refer to the penetration testing methodology and the importance of a comprehensive vulnerability management program to maintain security posture.
Lastly, organizations should stay informed about the latest security threats and adopt a strategic approach to their security practices to mitigate risks effectively.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
.webp)