System administrators, software providers and other IT professionals are now urged to patch another vulnerability in Log4j, this time a high-severity denial-of-service vulnerability.
The Apache Foundation released Log4j 2.17.0 late Friday, about a week after a critical remote code execution vulnerability was found in the popular logging tool that has impacted every corner of the IT ecosystem.
On its website, the Foundation says earlier versions of Log4j 2 don’t protect against “uncontrolled recursion from self-referential lookups.”
“When the logging configuration uses a non-default Pattern Layout with a Context Lookup (for example, $${ctx:loginId}), attackers with control over Thread Context Map (MDC) input data can craft malicious input data that contains a recursive lookup, resulting in a StackOverflowError that will terminate the process. This is also known as a DOS (Denial of Service) attack,” reads the foundation’s advisory.
The Foundation recommends users of Java 8 or later upgrade to the new release or following these mitigation steps:
- In PatternLayout in the logging configuration, replace Context Lookups like ${ctx:loginId} or $${ctx:loginId} with Thread Context Map patterns (%X, %mdc, or %MDC).
- Otherwise, in the configuration, remove references to Context Lookups like ${ctx:loginId} or $${ctx:loginId} where they originate from sources external to the application such as HTTP headers or user input.
The Apache Foundation also notes that only the Log4j-core JAR file is impacted by this particular vulnerability, so applications using only the Log4j-api JAR file without the Log4j-core JAR file are not impacted.
“Also note that Apache Log4j is the only Logging Services subproject affected by this vulnerability. Other projects like Log4net and Log4cxx are not impacted by this,” the foundation says.
This comes after the Foundation issued a second fix to Log4Shell last week that completely disables access to JNDI lookup by default and fixes a remote denial-of-service vulnerability.
According to The Apache Foundation, 2.15.0 restricts JNDI LDAP lookups to localhost by default, but 2.16.0 disables access to JNDI by default, and lookups now need to be enabled explicitly.
That update also limits the protocols by default to only Java, LDAP and LDAPS and limits the LDAP protocols to only accessing Java primitive objects. Hosts other than the local host need to be explicitly allowed, the organization says in an advisory.
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