Spring Security Vulnerability Exposes Valid Usernames to Attackers

A newly identified security vulnerability, CVE-2025-22234, has exposed a critical weakness in the widely-used Spring Security framework.

According to the HeroDevs report, affecting several versions of the spring-security-crypto package, this flaw makes it possible for attackers to discern valid usernames through observable differences in login response times—an avenue for so-called “timing attacks.”

Spring Security is a cornerstone Java framework for most enterprise applications, enabling authentication, authorization, and various other security measures.

It integrates tightly with the Spring ecosystem and is valued for its flexibility and robust configuration options.

However, this latest vulnerability undermines those very protections, highlighting the delicate balance between performance and security.

CVE-2025-22234: Details of the Vulnerability

The core issue arises from a recent patch (CVE-2025-22228) designed to address a different bug in the spring-security-crypto package.

Unfortunately, this update inadvertently weakened existing mitigations against timing attacks in the DaoAuthenticationProvider.

Specifically, when using the BCrypt password encoder, requests with passwords longer than 72 characters would cause the encoder to throw an exception.

This difference in system behavior makes it possible for attackers to measure how long the authentication process takes and infer whether a username exists in the system.

Previously, Spring Security always performed a password check, regardless of the username’s validity.

This strategy ensured that login response times were consistent, thus preventing attackers from distinguishing between valid and invalid usernames.

The new behavior, however, creates an observable disparity, increasing the risk of information exposure.

Technical Impact

• Who is affected: All users of Spring Security versions 5.7.16, 5.8.18, 6.0.16, 6.1.14, 6.2.10, 6.3.8, and 6.4.4 using DaoAuthenticationProvider with BCryptPasswordEncoder.
• Attack scenario: An attacker submits login attempts with various usernames and measures response times. A faster response indicates an invalid username, while a slower one signals a valid username (even if the password is wrong), thus facilitating username enumeration.
• Remediation: The vulnerability has been fixed in the Never-Ending Support (NES) releases v5.7.18 and v5.8.21. Users are strongly advised to update immediately.

Upgrading to the latest patched version of Spring Security is the best line of defense. Developers should test systems to ensure consistent response times irrespective of username validity and password length.