Once you’re done, cross your fingers and hope the ASF has found all the flaws that need immediate fixes so we can all stop worrying about this piece of software over Christmas. In PatternLayout in the logging configuration, replace Context Lookups like $ where they originate from sources external to the application such as HTTP headers or user input.The ASF has also outlined the following mitigations: You know the drill by now: download the latest version 2.17.0 of Log4J, here, and install it everywhere Log4j runs, which of course turns out to be everywhere (including in some hard-to-find places). This leads to an infinite recursion and a DoS condition on the server. However, when the nested variable references the variable being replaced, the recursion is called with the same string. Log4J v1 is also vulnerable to other RCE vectors and we recommend you migrate to Log4J 2.16.0 where possible.When a nested variable is substituted by the StrSubstitutor class, it recursively calls the substitute() class. Please note that Log4J v1 is End Of Life (EOL) and will not receive patches for this issue. To use this playbook, create a custom list called 'log4jhostsandfiles' with a format in which the first column should be an IP or hostname of a potentially affected log4j host, the second should be the operating system family (either unix or windows), and the third should be a full path to a file to delete if there are. Users who want to avoid attacker-controlled JNDI lookups but cannot upgrade to 2.16.0 must ensure that no such lookups resolve to attacker-provided data and ensure that the the JndiLookup class is not loaded. More information is available on the GitHub Security Advisory for CVE-2021-45046. This problem is being tracked as CVE-2021-45046. The Apache Logging Services team provided updated mitigation advice upon the release of version 2.16.0, which disables JNDI by default and completely removes support for message lookups.Įven in version 2.15.0, lookups used in layouts to provide specific pieces of context information will still recursively resolve, possibly triggering JNDI lookups. Remediation Advice Updated advice for version 2.16.0 The 4j:log4j-api should be kept at the same version as the 4j:log4j-core package to ensure compatability if in use. Only the 4j:log4j-core package is directly affected by this vulnerability. Security releasesĪdditional backports of this fix have been made available in versions 2.3.1, 2.12.2, and 2.12.3 Affected packages The v1 branch of Log4J which is considered End Of Life (EOL) is vulnerable to other RCE vectors so the recommendation is to still update to 2.16.0 where possible. Affected versionsĪny Log4J version prior to v2.15.0 is affected to this specific issue. This includes untrusted data included in logged errors such as exception traces, authentication failures, and other unexpected vectors of user controlled input. Logging untrusted or user controlled data with a vulnerable version of Log4J may result in Remote Code Execution (RCE) against your application. For more information, see the Updated advice for version 2.16.0 section of this advisory. Log4j version 2.15.0 contained an earlier fix for the vulnerability, but that patch did not disable attacker-controlled JNDI lookups in all situations. From log4j 2.16.0, this behavior has been disabled by default. An attacker who can control log messages or log message parameters can execute arbitrary code loaded from LDAP servers when message lookup substitution is enabled. Log4j versions prior to 2.16.0 are subject to a remote code execution vulnerability via the ldap JNDI parser.Īs per Apache's Log4j security guide: Apache Log4j2 <=2.14.1 JNDI features used in configuration, log messages, and parameters do not protect against attacker controlled LDAP and other JNDI related endpoints.
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