CVE-2020-7779 in djvalidator
Summary
by MITRE • 11/26/2020
All versions of package djvalidator are vulnerable to Regular Expression Denial of Service (ReDoS) by sending crafted invalid emails - for example, --@------------------------------------------------------------------------------------------------------------------------!.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 12/10/2020
The vulnerability identified as CVE-2020-7779 affects the djvalidator package, a popular Django validation library used for email address validation in web applications. This issue represents a classic Regular Expression Denial of Service (ReDoS) vulnerability that exploits the inefficient handling of certain input patterns within the email validation logic. The vulnerability manifests when maliciously crafted email addresses are submitted to applications using this package, specifically those containing repeated hyphens and special characters that cause the regular expression engine to enter into a catastrophic backtracking state. The crafted input string --@- -----------------------------------------------------------------------------------------------------------------------! demonstrates how a seemingly simple email validation can be exploited through carefully constructed character sequences that trigger exponential time complexity in the regular expression matching process.
The technical flaw stems from the implementation of regular expressions within the djvalidator package that fail to properly handle certain patterns that cause the regex engine to perform an excessive number of backtracking operations. This type of vulnerability falls under CWE-400, which specifically addresses the improper handling of regular expressions that can lead to resource exhaustion and denial of service conditions. When an attacker submits a malformed email address that matches the vulnerable regex pattern, the validation process becomes exponentially slower, consuming increasing amounts of CPU resources and potentially causing the application to become unresponsive or crash entirely. The vulnerability is particularly dangerous because email validation is a common operation that occurs frequently in web applications, making it an attractive target for attackers seeking to disrupt service availability.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can be exploited in various attack vectors including web application denial of service, resource exhaustion attacks, and potential service disruption for legitimate users. Applications that rely on djvalidator for email input validation become vulnerable to attackers who can craft specific email addresses to cause the validation process to consume excessive computational resources, effectively creating a resource starvation condition. This vulnerability can be particularly problematic in high-traffic applications where email validation occurs frequently, as the impact can compound and affect overall system performance and availability. The attack can be executed with minimal resources and technical expertise, making it a significant concern for organizations that depend on this validation library for user input sanitization.
Mitigation strategies for CVE-2020-7779 should focus on both immediate remediation and long-term architectural improvements to prevent similar vulnerabilities. The most direct solution involves updating to a patched version of the djvalidator package that addresses the regular expression implementation issues. Organizations should also implement input validation rate limiting and resource monitoring to detect and prevent exploitation attempts. Additionally, the use of more efficient validation libraries that employ bounded regular expressions or alternative validation approaches such as finite state machines can provide better protection against ReDoS attacks. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 which covers network denial of service attacks, and T1595.001 which addresses reconnaissance through information gathering. Organizations should also consider implementing web application firewalls that can detect and block malicious input patterns before they reach the vulnerable validation logic, and establish proper input sanitization processes that validate and sanitize all user-provided data at multiple layers of the application architecture.