CVE-2026-22747: Spring Security Auth Bypass Vulnerability

CVE-2026-22747 Overview

A certificate validation bypass vulnerability exists in Spring Security versions 7.0.0 through 7.0.4. The SubjectX500PrincipalExtractor component does not correctly handle certain malformed X.509 certificate Common Name (CN) values, which can lead to reading the wrong value for the username. In a carefully crafted certificate, this vulnerability allows an attacker to impersonate another user, potentially gaining unauthorized access to protected resources.

Critical Impact

Attackers with low privileges can craft malicious X.509 certificates to impersonate other users, bypassing authentication controls in applications using Spring Security's X.509 certificate authentication.

Affected Products

• Spring Security 7.0.0
• Spring Security 7.0.1
• Spring Security 7.0.2
• Spring Security 7.0.3
• Spring Security 7.0.4

Discovery Timeline

• 2026-04-22 - CVE-2026-22747 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-22747

Vulnerability Analysis

This vulnerability is classified under CWE-297 (Improper Validation of Certificate with Host Mismatch), indicating a fundamental flaw in how Spring Security processes X.509 certificate subject information. The SubjectX500PrincipalExtractor class is responsible for extracting the principal (username) from X.509 certificates during client certificate authentication flows.

The core issue lies in the parsing logic that processes the Distinguished Name (DN) string from the certificate's subject field. When a certificate contains specially crafted CN values with certain malformed characters or escape sequences, the extraction logic fails to properly parse the boundary between CN fields, potentially returning an incorrect username value.

This improper certificate validation allows an attacker with the ability to present a client certificate (requiring low privileges in the form of certificate enrollment capabilities) to craft a certificate that tricks the application into authenticating them as a different user.

Root Cause

The root cause stems from insufficient input validation within the SubjectX500PrincipalExtractor when parsing X.500 Distinguished Names. The extractor does not properly handle edge cases in DN formatting, particularly around escaped characters, multi-valued RDNs (Relative Distinguished Names), or specially formatted CN attributes. When these malformed values are encountered, the parsing algorithm may extract a substring that corresponds to a different user's identity rather than the attacker's actual CN.

Attack Vector

The attack requires network access and involves the following exploitation path:

1. An attacker obtains a valid client certificate from a trusted Certificate Authority (CA) that the target application trusts
2. The attacker crafts a certificate signing request (CSR) with a specially formatted CN value containing parsing-confusing characters
3. When the malicious certificate is presented during TLS client authentication, Spring Security's SubjectX500PrincipalExtractor parses the malformed CN
4. Due to the parsing flaw, the extracted username corresponds to a victim user instead of the attacker
5. The attacker is authenticated as the victim user, gaining access to their resources and permissions

The attack requires the attacker to have low-level privileges (ability to obtain certificates from a trusted CA) and operates over the network. No user interaction is required once the malicious certificate is presented.

Detection Methods for CVE-2026-22747

Indicators of Compromise

• Unusual authentication events where certificate subject DN contains non-standard characters or escape sequences
• Multiple successful authentications from certificates with similar but slightly different CN formatting
• Authentication logs showing users accessing resources from unexpected certificate serial numbers
• Certificate validation logs indicating parsing anomalies in X.500 DN strings

Detection Strategies

• Monitor Spring Security authentication logs for X.509 certificate authentication events with unusual DN patterns
• Implement certificate pinning or additional validation beyond Spring Security's default extraction logic
• Deploy application-level logging that captures both the raw certificate DN and the extracted principal for comparison
• Use SentinelOne's runtime protection to detect anomalous authentication patterns in Java applications

Monitoring Recommendations

• Enable detailed logging for Spring Security's X.509 authentication components
• Implement alerting on authentication events where the extracted username differs from expected certificate metadata
• Review Certificate Authority logs for CSRs with unusual CN formatting
• Correlate authentication events with expected user behavior patterns to identify impersonation attempts

How to Mitigate CVE-2026-22747

Immediate Actions Required

• Upgrade Spring Security to a version beyond 7.0.4 that contains the fix for this vulnerability
• Review authentication logs for signs of exploitation during the exposure window
• Implement additional certificate validation logic as defense-in-depth
• Consider temporarily disabling X.509 client certificate authentication if not critical to operations

Patch Information

Spring has released a security advisory for this vulnerability. Organizations should upgrade to a patched version of Spring Security as soon as one becomes available. Refer to the Spring Security Advisory CVE-2026-22747 for official patch information and updated version details.

Workarounds

• Implement a custom PrincipalExtractor that performs strict validation of CN values before extraction
• Add post-authentication validation that compares extracted principals against expected certificate metadata
• Restrict the set of trusted Certificate Authorities to minimize the attack surface
• Deploy Web Application Firewall (WAF) rules to detect and block certificates with suspicious DN formatting
• Consider implementing certificate allowlisting for high-privilege accounts

# Configuration example - Enable detailed Spring Security logging for monitoring
# Add to application.properties or application.yml

# Enable debug logging for X.509 authentication
logging.level.org.springframework.security.web.authentication.preauth.x509=DEBUG
logging.level.org.springframework.security.core.userdetails=DEBUG

# Log certificate details for forensic analysis
logging.level.org.springframework.security.web.authentication=TRACE