Sovereign Cloud Stack

Sovereign Cloud Stack (SCS) ist eine offene, föderierbare und modulare Cloud- und Containerplattform auf Basis von Open-Source-Software.

Sovereign Cloud Stack Security Advisory log4j

Christian Berendt, Kurt Garloff, Felix Kronlage-Dammers 13. Dezember 2021

The vulnerability

On Fri, 2021-12-10, a design issue in the very popular Java library log4j was reported and assigned CVE-2021-44228 with a CVSS score of 10, which is the highest possible score and thus means that this is a very critical vulnerability. In short, log4j interprets strings that are being submitted to it causing lookups via the JNDI interface (intended e.g. to do LDAP name resolution). If attackers can cause log4j to log attacker controlled strings, these can be used to trigger these lookups and cause arbitrary java code to be loaded and executed. This can be used to gain access to the application that uses log4j and the container/VM that the application is running in. As log4j is so popular, many Java applications are affected. At this point in time, all log4j versions prior to log4j2-2.15(-rc2) are affected.

Our German readers might want to read the excellent summary in the BSI advisory.

Usage of log4j in SCS

The main components of Sovereign Cloud Stack do not use Java. However, there are Java tools used at a few places:

  1. Keycloak (Identity broker)
  2. Nexus (Mirror manager)
  3. Elasticsearch (Log analysis tool)

Neither keycloak nor nexus are affected by the log4j vulnerability.

However, Elasticsearch does use log4j. Elasticsearch is rolled out in a container on the SCS compute nodes by default in SCS deployments to allow for log analysis.

Potential impact

Normal users do not interact with the Elasticsearch functionality in SCS; only operators have access to it. An issue that can be abused by operators is not a serious threat to SCS environments, as in all practical setups, the operators have more privileges to affect the environment than they could gain by exploiting vulnerabilities in Elasticsearch. This might only be different in environments with very large operational teams and a very fine-grained operational access role model.

However, we can at this point not exclude the possibility that a name controlled by the user (such as the name from a resource at OpenStack or Kubernetes level) gets logged and later on processed by ElasticSearch and logged again via log4j. If so, a user could cause undesired actions within the ElasticSearch container. If a potential attacker could in addition find another exploit to escape the container confinement, he could take over the SCS deployment.

Mitigation and fix

Until a new version of the Elasticsearch container that uses a fixed log4j is available, we recommend applying the following change:

  1. Change the configuration repository. In environments/kolla/configuration.yml, add -Dlog4j2.formatMsgNoLookups=true to the JVM startup paramters:

       es_java_opts: "-Dlog4j2.formatMsgNoLookups=true {% if es_heap_size %}-Xms{{ es_heap_size }} -Xmx{{ es_heap_size }}{%endif%}"
  2. Roll out the changes:
    • If you are not using Celery:
        osism-manager configuration
    • If you are using Celery:
        osism apply configuration
  3. (Re)deploy Elasticsearch:
    • If you are not using Celery:
        osism-kolla deploy elastisearch
    • If you are using Celery:
        osism apply elasticsearch

This causes log4j to no longer interpret the input in ways that lookups can be triggered and thus reliably avoids the vulnerability. Please note that this setting log4j2.formatMsgNoLookups is only available in log4j2 >= 2.10.0, which is fortunately the case in the Elasticsearch container.

When a new Elasticsearch container built with the fixed log4j (2.16 or better 2.17+) becomes available, we’ll issue a new advisory that describes the deployment of the new container.

Update 2021-12-21: Fix still valid

Meanwhile, two more security issues around log4j have been reported: CVE-2021-45046 and CVE-2021-45105. The former is a context lookup vulnerability (as a variation to the JNDI lookup vulnerability) while the latter is a Denial of Service attack by causing an infinite recursion on the context lookup.

The recommended setting log4j2.formatMsgNoLookups=true is still fully mitigating the issues in our environment.

The es_java_opts setting has been configured in the upstream OSISM/ansible_defaults repository meanwhile (commit c84f87a6106dd53d08447ac7d5a24b2677da38f0), so fresh deployments of SCS testbeds or production environments get the mitigation automatically. You can validate this by logging in to one of your compute nodes and checking the jvm parameters in the process list (elastic search container). You should find -Dlog4j2.formatMsgNoLookups=true in the parameter list.

Sovereign Cloud Stack Security Contact

Please contact the SCS project management team at project at scs dot sovereignit dot de to ask security questions or report security issues.

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