CVE-2024-38827: String Locale Auth Bypass Vulnerability

CVE-2024-38827 Overview

CVE-2024-38827 is an authorization bypass vulnerability in Spring Security caused by locale-dependent behavior in Java's String.toLowerCase() and String.toUpperCase() methods. When these methods are used for authorization rule comparisons, certain locale-specific character transformations can cause authorization checks to fail unexpectedly, potentially allowing unauthorized access to protected resources.

Critical Impact

Authorization rules may not work properly due to locale-dependent string case conversions, potentially allowing attackers to bypass access controls in affected Spring Security applications.

Affected Products

• Spring Security (versions using locale-dependent case conversion for authorization)
• Applications using Spring Security with locale-sensitive authorization rules
• NetApp products (as referenced in NetApp Security Advisory NTAP-20250124-0007)

Discovery Timeline

• 2024-12-02 - CVE CVE-2024-38827 published to NVD
• 2025-01-24 - Last updated in NVD database

Technical Details for CVE-2024-38827

Vulnerability Analysis

This vulnerability falls under CWE-639 (Authorization Bypass Through User-Controlled Key) and stems from the improper use of locale-dependent string transformation methods in authorization logic. Java's String.toLowerCase() and String.toUpperCase() methods, when called without an explicit Locale parameter, use the default system locale. This can lead to unexpected behavior in certain locales where character case transformations differ from standard ASCII expectations.

The most notable example is the Turkish locale, where the lowercase of 'I' is 'ı' (dotless i) rather than 'i', and the uppercase of 'i' is 'İ' (dotted I) rather than 'I'. When Spring Security's authorization rules rely on case-insensitive string comparisons using these methods, attackers operating in or targeting systems with non-standard locales may be able to craft requests that bypass intended access controls.

The network-based attack vector requires precise conditions to exploit, as the attacker must target a system where the locale configuration creates discrepancies in the authorization rule matching logic.

Root Cause

The root cause is the use of String.toLowerCase() and String.toUpperCase() without specifying Locale.ROOT or Locale.ENGLISH. When the default locale is used, certain languages have locale-specific casing rules that cause string comparisons to produce unexpected results. This is particularly problematic in security-sensitive contexts like authorization rule evaluation, where consistent string matching is essential for proper access control enforcement.

Attack Vector

The attack vector is network-based and requires specific conditions to be met. An attacker would need to:

1. Identify a Spring Security application using locale-dependent string case conversion in authorization rules
2. Determine or influence the target system's locale configuration
3. Craft HTTP requests with resource paths or authorization tokens that exploit locale-specific character transformations
4. Bypass authorization checks by leveraging the mismatch between the expected lowercase/uppercase form and the actual locale-dependent transformation

The vulnerability exploitation path involves targeting authorization endpoints where case-insensitive matching is performed on user-controlled input such as URL paths, role names, or permission identifiers. For detailed technical information, refer to the Spring Security CVE-2024-38827 advisory.

Detection Methods for CVE-2024-38827

Indicators of Compromise

• Unusual access patterns to protected resources from systems with non-standard locale configurations
• Authorization log entries showing access grants that should have been denied based on configured rules
• Requests containing characters that have locale-specific case transformations (e.g., Turkish dotted/dotless I variants)
• Anomalous successful authentication or authorization events correlated with locale-related headers

Detection Strategies

• Review application logs for authorization decisions that don't match expected behavior based on configured rules
• Monitor for HTTP requests containing characters known to have locale-dependent case transformations
• Implement logging that captures both the original request and the normalized form used for authorization comparison
• Audit Spring Security configuration for use of locale-dependent string methods in custom authorization rules

Monitoring Recommendations

• Enable detailed Spring Security debug logging to track authorization rule evaluation
• Monitor for unusual patterns in the Accept-Language headers that may indicate locale manipulation attempts
• Implement alerting on authorization bypass indicators in security information and event management (SIEM) systems
• Conduct regular audits of authorization logs to identify potential bypass attempts

How to Mitigate CVE-2024-38827

Immediate Actions Required

• Review all custom Spring Security authorization logic for use of String.toLowerCase() and String.toUpperCase() without explicit locale parameters
• Update Spring Security to the latest patched version as recommended in the official advisory
• Audit application code for similar locale-dependent string comparison patterns in security-critical paths
• Consider implementing additional authorization checks that do not rely on case-insensitive string matching

Patch Information

VMware/Spring has released security patches to address this vulnerability. Refer to the Spring Security CVE-2024-38827 advisory for specific version information and upgrade instructions. NetApp has also published guidance in their security advisory NTAP-20250124-0007 for affected NetApp products.

Workarounds

• Replace calls to String.toLowerCase() with String.toLowerCase(Locale.ROOT) in all authorization-related code
• Replace calls to String.toUpperCase() with String.toUpperCase(Locale.ROOT) in all authorization-related code
• Implement explicit locale specification in all security-sensitive string comparisons
• Consider using equalsIgnoreCase() alternatives that are locale-independent or implementing custom comparison logic

# Review Spring Security configuration for locale-sensitive patterns
# Search for potentially vulnerable code patterns in your codebase:
grep -r "toLowerCase()" --include="*.java" | grep -v "Locale"
grep -r "toUpperCase()" --include="*.java" | grep -v "Locale"

# Ensure JVM is configured with a consistent default locale if patching is delayed
# Add to JVM startup options:
# -Duser.language=en -Duser.country=US