Summary pgjdbc is vulnerable to a client-side denial of service during SCRAM-SHA-256 authentication.

Impact A malicious server can instruct the driver to perform SCRAM authentication with a very large iteration count. With a large enough value, the client spends an unbounded amount of CPU time inside PBKDF2 before authentication can fail. A single attempt ties up a CPU core. Repeated or concurrent attempts exhaust client CPU and can wedge connection pools.

In affected versions, loginTimeout did not fully mitigate this problem. When loginTimeout expired, the caller could stop waiting, but the worker thread performing the connection attempt could continue running and burning CPU inside the SCRAM PBKDF2 computation.

This issue affects availability. It does not provide authentication bypass, privilege escalation, or direct password disclosure.

A user is vulnerable when all of the following are true:

1. The connection uses SCRAM-SHA-256 authentication. 2. The client reaches a malicious, compromised, or attacker-controlled PostgreSQL endpoint. 3. That endpoint sends a very large SCRAM PBKDF2 iteration count in the server-first-message.

In practice, that can happen in these situations:

- the application lets end users or tenants supply their own database connection details (as in many BI, reporting, analytics, ETL, and low-code platforms), so a user can point the shared client host at a server they control - the application accepts connection strings, hostnames, or JDBC URLs from user input, configuration uploaded by users, or other untrusted sources - the application is configured to connect to a PostgreSQL server that is itself malicious or later becomes compromised - the application connects through an untrusted proxy, relay, tunnel, bastion, or connection-pooling service that can act as the PostgreSQL server - an attacker can redirect the client to a fake PostgreSQL endpoint by manipulating DNS, service discovery, Kubernetes service resolution, /etc/hosts, environment variables, or similar indirection - an active network attacker on the path can impersonate the server because the connection does not strongly verify server identity (for example, sslmode lower than verify-full, or trusting a CA that signs hosts outside the operator's control)

The issue is more damaging when the application uses connection retries, many parallel connection attempts, or loginTimeout and assumes the timeout fully stops the work.

Patches The patch introduces a new connection property, scramMaxIterations, with a default of 100K. The client now rejects SCRAM server messages that advertise more PBKDF2 iterations than the configured cap before starting the PBKDF2 computation begins.

Workarounds

Until a patched version of pgjdbc is deployed, the following measures reduce exposure:

1. Only connect to trusted PostgreSQL servers whose identity is verified. Connect only to trusted PostgreSQL servers, and verify server identity with TLS using sslmode=verify-full and a trusted CA. TLS without certificate and hostname verification is not sufficient as an active network attacker can still impersonate the server.

2. Do not rely on loginTimeout as a complete mitigation on unpatched versions. On affected versions, loginTimeout can stop the waiting caller while the worker thread continues spending CPU.

3. Avoid SCRAM on untrusted or interceptable connection paths. For those paths, use an authentication method that does not let the server choose a SCRAM PBKDF2 iteration count.

4. Reduce blast radius operationally. Limit parallel connection attempts, add retry backoff, isolate connection establishment in a separate worker or process when possible, and apply CPU or container limits where appropriate.

5. On trusted servers you control, keep SCRAM iteration counts at ordinary values. This does not defend against an attacker-controlled server, but it avoids unnecessary client cost when talking to legitimate servers.

Vulnerability

PreparedStatement.setText(int, InputStream) and

PreparedStatemet.setBytea(int, InputStream)

will create a temporary file if the InputStream is larger than 51k

Example of vulnerable code:

java String s = "some very large string greater than 51200 bytes";

PreparedStatement.setInputStream(1, new ByteArrayInputStream(s.getBytes()) ); This will create a temporary file which is readable by other users on Unix like systems, but not MacOS.

Impact On Unix like systems, the system's temporary directory is shared between all users on that system. Because of this, when files and directories are written into this directory they are, by default, readable by other users on that same system.

This vulnerability does not allow other users to overwrite the contents of these directories or files. This is purely an information disclosure vulnerability.

When analyzing the impact of this vulnerability, here are the important questions to ask:

Is the driver running in an environment where the OS has other untrusted users. If yes, and you answered 'yes' to question 1, this vulnerability impacts you. If no, this vulnerability does not impact you. Patches Because certain JDK file system APIs were only added in JDK 1.7, this this fix is dependent upon the version of the JDK you are using.

Java 1.8 and higher users: this vulnerability is fixed in 42.2.27, 42.3.8, 42.4.3, 42.5.1 Java 1.7 users: this vulnerability is fixed in 42.2.27.jre7 Java 1.6 and lower users: no patch is available; you must use the workaround below. Workarounds If you are unable to patch, or are stuck running on Java 1.6, specifying the java.io.tmpdir system environment variable to a directory that is exclusively owned by the executing user will fix this vulnerability.

References CWE-200: Exposure of Sensitive Information to an Unauthorized Actor Fix commit https://github.com/pgjdbc/pgjdbc/commit/9008dc9aade6dbfe4efafcd6872ebc55f4699cf5 Similar Vulnerabilities Google Guava - https://github.com/google/guava/issues/4011 Apache Ant - https://nvd.nist.gov/vuln/detail/CVE-2020-1945 JetBrains Kotlin Compiler - https://nvd.nist.gov/vuln/detail/CVE-2020-15824