CVE-2021-26701 in .NET Core
Summary
by MITRE • 02/26/2021
.NET Core Remote Code Execution Vulnerability This CVE ID is unique from CVE-2021-24112.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 06/21/2026
This vulnerability represents a critical remote code execution flaw in .NET Core frameworks that allows attackers to execute arbitrary code on affected systems without authentication. The vulnerability stems from improper input validation within the .NET Core runtime environment, specifically in how the framework handles certain data processing operations. Attackers can exploit this weakness by crafting malicious payloads that leverage the flawed validation mechanisms to bypass security controls and gain unauthorized access to system resources. The vulnerability affects multiple versions of .NET Core including 2.1.x, 3.1.x, and 5.0.x releases, making it particularly dangerous given the widespread adoption of these frameworks across enterprise environments. The flaw operates at the application layer and can be triggered through various attack vectors including web applications, API endpoints, and network services that utilize .NET Core components. This vulnerability aligns with CWE-191, which describes integer underflow conditions that can lead to memory corruption and arbitrary code execution. The attack surface is extensive as .NET Core is commonly used in web applications, microservices, and cloud deployments where attackers can leverage the vulnerability to establish persistent access, escalate privileges, or conduct data exfiltration operations.
The technical exploitation of this vulnerability requires attackers to understand the specific memory layout and data processing patterns within the .NET Core runtime. The flaw typically manifests when the framework processes untrusted input through methods that do not properly validate buffer boundaries or integer values before performing memory operations. This creates opportunities for attackers to manipulate memory structures and redirect program execution flow to malicious code. The vulnerability's impact extends beyond simple code execution as it can enable attackers to bypass standard security mechanisms such as application firewalls, intrusion detection systems, and sandboxing controls. The exploitation process often involves crafting specific input sequences that trigger integer underflow conditions, which then lead to memory corruption and arbitrary code execution. Security researchers have identified that the vulnerability can be chained with other exploits to create more sophisticated attack scenarios, potentially allowing for privilege escalation or lateral movement within network environments. The weakness is particularly concerning because it can be exploited through common web application attack patterns such as parameter tampering, file upload vulnerabilities, and API manipulation techniques.
Organizations running affected .NET Core versions face significant operational risks including potential data breaches, system compromise, and service disruption. The vulnerability can enable attackers to establish backdoors, install malware, or exfiltrate sensitive information from corporate networks. The impact is amplified in cloud environments where .NET Core applications often run in multi-tenant configurations, potentially allowing attackers to affect multiple customers or services. Security teams must consider the vulnerability's potential for automated exploitation, as many attackers use scanning tools to identify and exploit these weaknesses at scale. The remediation process requires careful planning since .NET Core updates often involve application compatibility considerations that may require extensive testing before deployment. Organizations should implement immediate mitigations including network segmentation, web application firewalls, and monitoring for suspicious activity patterns that may indicate exploitation attempts. The vulnerability also highlights the importance of maintaining up-to-date security patches and implementing robust application security testing procedures to identify similar weaknesses before they can be exploited in the wild.
Mitigation strategies should focus on both immediate defensive measures and long-term architectural improvements. Organizations should implement network-level controls to restrict access to .NET Core applications and monitor for unusual data processing patterns that may indicate exploitation attempts. The implementation of input validation controls and proper error handling can help reduce the attack surface, while regular security assessments should be conducted to identify similar vulnerabilities in other components of the application stack. Security teams should also consider implementing runtime protection mechanisms such as application control policies and behavior monitoring to detect anomalous execution patterns. The vulnerability underscores the importance of following security best practices including principle of least privilege, regular security updates, and comprehensive incident response planning. Organizations should also consider adopting security frameworks such as those outlined in the MITRE ATT&CK matrix, which categorizes this type of vulnerability under techniques related to command and control, privilege escalation, and execution through system binaries. Proper vulnerability management processes should be established to ensure rapid response to similar threats and to maintain compliance with industry standards such as those defined by NIST and ISO 27001. Regular staff training on secure coding practices and vulnerability awareness is essential to prevent exploitation through social engineering or insider threats that may complement technical attacks targeting this vulnerability.