CVE-2026-27830 is a critical deserialization of untrusted data vulnerability (CWE-502) affecting the c3p0 JDBC connection pooling library versions before 0.12.0. The vulnerability centers on the userOverridesAsString property of several c3p0 ConnectionPoolDataSource implementations, which was stored as a hex-encoded serialized Java object representing a Map<String, Map<String,String>>. Because this property could be reset or manipulated by attackers, maliciously crafted serialized objects or javax.naming.Reference instances could be injected. Upon deserialization, these objects could execute arbitrary code on the application's classpath. The threat is exacerbated by c3p0's dependency on mchange-commons-java, which includes early JNDI implementation code with insufficient restrictions on remote factoryClassLocation values. This allows attackers to embed JNDI references that cause the application to download and execute malicious code from remote servers. The vulnerability does not require user interaction but does require some level of privilege to reset the property or inject malicious serialized data. The fix in c3p0 0.12.0 replaces the unsafe serialized object format with a safe CSV-based format for userOverridesAsString and upgrades mchange-commons-java to version 0.4.0 or later, which enforces restrictive configuration parameters and name guards to prevent remote JNDI injection. No mitigations exist for earlier versions, making upgrade imperative. This vulnerability highlights the dangers of using Java serialization for writable JavaBean properties exposed across JNDI interfaces.

The impact of CVE-2026-27830 is severe, as it enables remote code execution within the context of applications using vulnerable c3p0 versions. Exploitation could lead to full compromise of affected systems, including unauthorized access to sensitive data, disruption of service, and lateral movement within networks. Because c3p0 is widely used in Java applications for database connection pooling, many enterprise applications, middleware, and backend services are at risk. The vulnerability's exploitation does not require user interaction but does require the ability to reset or influence the userOverridesAsString property, which may be possible in multi-tenant environments or through other injection vectors. The dependency on mchange-commons-java's flawed JNDI implementation further increases the attack surface by enabling remote code loading, making this vulnerability particularly dangerous in internet-facing or poorly segmented environments. Organizations failing to upgrade risk data breaches, service outages, and potential regulatory penalties due to compromised systems.

The primary mitigation is to upgrade all c3p0 instances to version 0.12.0 or later, which replaces the vulnerable serialized object format with a safe CSV-based format and upgrades mchange-commons-java to a version that restricts remote JNDI references. Organizations should audit their Java applications to identify any usage of c3p0 versions prior to 0.12.0, especially in internet-facing or multi-tenant environments. If immediate upgrade is not possible, restrict access to management interfaces or configuration endpoints that could allow resetting the userOverridesAsString property. Employ network segmentation and firewall rules to limit outbound LDAP or RMI connections that could be used for malicious JNDI lookups. Monitor application logs for suspicious deserialization activity or unexpected JNDI lookups. Additionally, consider implementing Java security manager policies or runtime instrumentation to detect or block deserialization of untrusted data. Finally, review and harden all dependencies related to JNDI and serialization to reduce attack surface.