CVE-2025-6738: bicycleSharingServer SQL Injection Vulnerability

CVE-2025-6738 Overview

CVE-2025-6738 is a SQL injection vulnerability in the huija bicycleSharingServer project, a Java-based bike-sharing backend hosted on GitHub. The flaw resides in the userDao.selectUserByUserNameLike function within UserServiceImpl.java. Attackers can manipulate the Username argument to inject arbitrary SQL statements against the backing database. The attack is remotely exploitable and requires only low-level privileges on the application. Because the project uses a rolling release model, no fixed version identifier exists for affected or patched builds. The vulnerability has been publicly disclosed, and proof-of-concept details are available through VulDB and the project's GitHub issue tracker.

Critical Impact
Remote authenticated attackers can inject SQL through the Username parameter, exposing or modifying data stored in the bicycle sharing application's database.

Affected Products

huija bicycleSharingServer up to commit 7b8a3ba48ad618604abd4797d2e7cf3b5ac7625a
UserServiceImpl.java component invoking userDao.selectUserByUserNameLike
All rolling-release builds prior to a maintainer-provided fix commit

Discovery Timeline

2025-06-27 - CVE-2025-6738 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-6738

Vulnerability Analysis

The vulnerability is a SQL injection flaw [CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component] in the user lookup path of the application. The selectUserByUserNameLike method in the Data Access Object (DAO) layer accepts a Username string from the service layer and incorporates it directly into a SQL LIKE query. Because the input is not parameterized or sanitized, an attacker can supply SQL metacharacters that break out of the string literal and append arbitrary clauses.

Exploitation requires network access to the application and a low-privileged account to reach the authenticated user search functionality. Successful injection can leak user records, authentication material, or administrative data stored in the database. Depending on database privileges, attackers may also modify records or chain additional queries using stacked statements.

Root Cause

The root cause is unsafe string concatenation of untrusted input into a dynamic SQL statement within the DAO layer. The selectUserByUserNameLike query concatenates the Username parameter into a LIKE clause without using prepared statements or binding parameters. The application also fails to validate or escape SQL metacharacters before passing input to the persistence layer.

Attack Vector

An attacker sends a crafted HTTP request to the user search endpoint that routes to UserServiceImpl.selectUserByUserNameLike. The malicious Username value contains SQL control characters such as single quotes, comment sequences, or UNION SELECT clauses. The backend substitutes the payload directly into the SQL text, allowing the attacker to alter query logic, extract data from other tables, or enumerate the schema.

For technical details on reproduction, see the GitHub Issue Report and VulDB entry #314012.

Detection Methods for CVE-2025-6738

Indicators of Compromise

HTTP requests containing SQL metacharacters such as ', --, /*, or UNION SELECT in the Username parameter
Database error messages or stack traces referencing selectUserByUserNameLike in application logs
Unusually long or encoded Username values submitted to user search endpoints
Spikes in query execution time or row counts returned by the user lookup query

Detection Strategies

Deploy a web application firewall (WAF) rule set that inspects user search parameters for SQL injection signatures
Enable database query logging and alert on LIKE queries containing boolean tautologies or UNION operators
Add runtime application self-protection (RASP) hooks on the DAO layer to detect query structure changes
Review application logs for repeated 500-series responses from the user search endpoint

Monitoring Recommendations

Baseline normal query patterns for userDao.selectUserByUserNameLike and alert on deviations
Forward application and database logs to a centralized analytics platform for correlation
Monitor outbound database traffic for unexpected bulk data reads from the users table
Track authentication events for the low-privileged accounts most likely to be used for exploitation

How to Mitigate CVE-2025-6738

Immediate Actions Required

Audit the UserServiceImpl.java file and rewrite selectUserByUserNameLike to use parameterized queries or prepared statements
Restrict access to the user search endpoint to authenticated administrative roles where feasible
Apply input validation that rejects SQL metacharacters in the Username field before it reaches the DAO layer
Reduce database account privileges used by the application to the minimum required for normal operation

Patch Information

The project uses a rolling release model, and no fixed version identifier is published. Operators should track the upstream repository and apply the maintainer's remediation commit once available. Monitor the GitHub Issue Report for status updates. In the interim, apply the source-level fix directly by replacing concatenated SQL with MyBatis #{} placeholders or JDBC PreparedStatement bindings.

Workarounds

Place the application behind a WAF with SQL injection rulesets enabled for all request parameters
Disable or firewall off the user search endpoint until a code-level fix is deployed
Enforce strict allow-list validation on the Username field, permitting only alphanumeric characters and a limited punctuation set
Rotate database credentials and audit the users table for signs of unauthorized reads after exposure

bash

# Example WAF rule (ModSecurity) to block SQLi patterns in Username parameter
SecRule ARGS:Username "@rx (?i)(union(\s)+select|--|/\*|';|\bor\b\s+\d+=\d+)" \
  "id:1006738,phase:2,deny,status:403,msg:'Possible SQLi targeting CVE-2025-6738'"