CVE-2026-47303 in .NET
Summary
by MITRE • 07/14/2026
Authentication bypass by assumed-immutable data in ASP.NET Core allows an authorized attacker to elevate privileges over a network.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 07/14/2026
This vulnerability represents a critical authentication bypass flaw that exploits the trust placed in immutable data within ASP.NET Core applications, allowing authorized attackers to escalate their privileges through network-based attacks. The security weakness stems from the application's improper handling of data that should remain unchanged during the authentication process, creating opportunities for malicious actors to manipulate authentication tokens or session identifiers that are expected to be immutable. When developers assume that certain data elements cannot be modified or tampered with during authentication flows, they inadvertently create attack vectors where adversaries can exploit this assumption to gain unauthorized access to elevated privileges.
The technical implementation of this vulnerability typically involves attackers manipulating authentication tokens, claims, or session data that are processed by ASP.NET Core's authentication middleware. These components often rely on data integrity assumptions that when violated can lead to privilege escalation scenarios. The flaw commonly manifests in applications that use JWT tokens, cookie-based authentication, or other stateful authentication mechanisms where the system trusts certain data elements without proper validation or re-verification. Attackers can exploit this by crafting malicious requests that modify expected immutable fields within authentication payloads, potentially bypassing authorization checks and gaining access to resources or operations typically restricted to higher privilege users.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it can enable attackers to perform actions that should be restricted to administrators or privileged users. Network-based exploitation means that even if the initial attack vector is remote, the consequences can be severe in terms of data compromise, system integrity violations, and potential lateral movement within network environments. The vulnerability affects organizations running ASP.NET Core applications where authentication flows are implemented without proper validation of immutable data elements, creating persistent security gaps that can be exploited repeatedly by determined attackers.
Mitigation strategies should focus on implementing robust validation mechanisms for all data elements processed during authentication, regardless of their expected immutability status. Organizations must ensure that authentication tokens and session data undergo comprehensive verification before being accepted as valid, with particular attention to fields that are traditionally considered trusted or immutable. The implementation of proper input sanitization, cryptographic validation of tokens, and regular authentication flow reviews can significantly reduce the risk of exploitation. Additionally, implementing principle of least privilege controls, monitoring for anomalous authentication patterns, and conducting regular security assessments of authentication mechanisms aligns with industry best practices and helps address the underlying causes of such vulnerabilities.
This vulnerability type corresponds to CWE-284 Access Control Issues and specifically relates to improper access control mechanisms that trust data without verification. The exploitation patterns align with ATT&CK techniques including privilege escalation through authentication bypass and credential manipulation, where attackers leverage application trust assumptions to gain elevated system access. Organizations should implement comprehensive logging of authentication events and establish alerting mechanisms for suspicious token modifications or unexpected authentication behavior to detect potential exploitation attempts.
The security implications extend to compliance requirements and regulatory frameworks that mandate proper authentication controls and access management within applications. When applications fail to validate the integrity of authentication data, they create gaps in their security posture that can lead to significant breaches affecting user privacy, system integrity, and organizational security. Regular security training for development teams on proper authentication implementation practices and secure coding standards is essential to prevent similar vulnerabilities from being introduced during application development cycles.