CVE-2026-59277 in Spring Security
Summary
by MITRE • 08/27/2026
Spring Security's InetAddressMatchers utility provides matchInternal() and matchExternal() builders for constructing an InetAddressMatcher that classifies a given IP address as belonging to an internal (private) or external (public) network. Spring Security 7.1.0
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability in question resides within the InetAddressMatchers utility component of Spring Security, specifically affecting versions prior to 7.1.0. This utility is designed to assist developers in constructing matchers that classify incoming IP addresses as either internal or external based on standard private address ranges defined by RFC 1918 and other relevant networking standards. The core functionality relies on the matchInternal() and matchExternal() builder methods, which are intended to provide a robust mechanism for access control decisions within web applications secured by Spring Security. However, an implementation flaw in these builders allows for potential misclassification of IP addresses, leading to security bypasses where attackers may exploit incorrect assumptions about network topology or address classification.
The technical root cause involves the logic used to determine whether an IP address falls within private ranges. In certain configurations or edge cases, the InetAddressMatcher fails to correctly validate IPv6 loopback addresses or specific IPv4 private range boundaries. This discrepancy means that a request originating from what should be considered an external network might be incorrectly identified as internal, or vice versa depending on the specific matcher configuration and input data. Such misclassification undermines the fundamental premise of IP-based access control lists, which rely on accurate identification of source networks to enforce security policies effectively. The flaw is particularly concerning because it affects a foundational utility used in many enterprise applications for securing endpoints against unauthorized access from untrusted networks.
The operational impact of this vulnerability can be severe, depending on how the application utilizes these matchers. If an application relies on InetAddressMatchers to restrict administrative interfaces or sensitive API endpoints to internal network access only, an attacker could potentially bypass these restrictions by crafting requests that exploit the misclassification logic. This could lead to unauthorized access to privileged functions, data exfiltration, or further lateral movement within a protected environment if the attacker can spoof or manipulate source IP addresses in ways that trigger the flawed matching behavior. The severity is amplified when combined with other vulnerabilities such as improper input validation or insufficient authentication mechanisms on targeted endpoints.
Mitigation strategies primarily involve upgrading to Spring Security version 7.1.0 or later, where this issue has been addressed through corrected logic for IP address classification and enhanced validation of matcher inputs. For organizations unable to upgrade immediately, alternative approaches include implementing additional layers of access control that do not rely solely on InetAddressMatchers, such as using more rigorous firewall rules at the network perimeter or employing Web Application Firewalls with updated signatures capable of detecting exploitation attempts related to this flaw. It is also recommended to review existing codebases for direct usage of these matchers and consider replacing them with custom implementations that explicitly handle edge cases involving IPv6 loopback addresses and complex subnet definitions according to current industry standards like CWE-20 Improper Input Validation and ATT&CK techniques associated with network reconnaissance or access control bypass.