h2 is a pure-Python implementation of a HTTP/2 protocol stack. Prior to version 4.3.0, an HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls. This issue has been patched in version 4.3.0.

An issue was discovered in hyper v0.13.7. h2-0.2.4 Stream stacking occurs when the H2 component processes HTTP2 RST_STREAM frames. As a result, the memory and CPU usage are high which can lead to a Denial of Service (DoS).

The web-based admin console in H2 Database Engine before 2.2.220 can be started via the CLI with the argument -webAdminPassword, which allows the user to specify the password in cleartext for the web admin console. Consequently, a local user (or an attacker that has obtained local access through some means) would be able to discover the password by listing processes and their arguments. NOTE: the vendor states "This is not a vulnerability of H2 Console ... Passwords should never be passed on the command line and every qualified DBA or system administrator is expected to know that." Nonetheless, the issue was fixed in 2.2.220.

H2 Console before 2.1.210 allows remote attackers to execute arbitrary code via a jdbc:h2:mem JDBC URL containing the IGNORE_UNKNOWN_SETTINGS=TRUE;FORBID_CREATION=FALSE;INIT=RUNSCRIPT substring, a different vulnerability than CVE-2021-42392.

The org.h2.util.JdbcUtils.getConnection method of the H2 database takes as parameters the class name of the driver and URL of the database. An attacker may pass a JNDI driver name and a URL leading to a LDAP or RMI servers, causing remote code execution. This can be exploited through various attack vectors, most notably through the H2 Console which leads to unauthenticated remote code execution.

The package com.h2database:h2 from 1.4.198 and before 2.0.202 are vulnerable to XML External Entity (XXE) Injection via the org.h2.jdbc.JdbcSQLXML class object, when it receives parsed string data from org.h2.jdbc.JdbcResultSet.getSQLXML() method. If it executes the getSource() method when the parameter is DOMSource.class it will trigger the vulnerability.

An issue was discovered in H2 1.4.197. Insecure handling of permissions in the backup function allows attackers to read sensitive files (outside of their permissions) via a symlink to a fake database file.

H2 1.4.197, as used in Datomic before 0.9.5697 and other products, allows remote code execution because CREATE ALIAS can execute arbitrary Java code. NOTE: the vendor's position is "h2 is not designed to be run outside of a secure environment."