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Log4shell: Justify log4j2.formatMsgNoLookups #62

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Dec 23, 2021
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Log4shell: Justify log4j2.formatMsgNoLookups #62

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9 changes: 5 additions & 4 deletions content/solr/security/2021-12-10-cve-2021-44228.md
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Expand Up @@ -15,10 +15,7 @@ Apache Solr releases prior to 7.4 (i.e. Solr 5, Solr 6, and Solr 7 through 7.3)

Solr's Prometheus Exporter uses Log4J as well but it does not log user input or data, so we don't see a risk there.

Apache Solr releases are *not* vulnerable to the followup **CVE-2021-45046** and **CVE-2021-45105**, because the MDC patterns used by Solr
are for the collection, shard, replica, core and node names, and a potential trace id, which are all sanitized
and injected into log files with "`%X`". Passing system property `log4j2.formatMsgNoLookups=true` (as described below)
is suitable to mitigate.
Solr is *not* vulnerable to the followup **CVE-2021-45046** and **CVE-2021-45105**. A listing of these and other CVEs with some justifications are listed in Solr's wiki: https://cwiki.apache.org/confluence/display/SOLR/SolrSecurity#SolrSecurity-SolrandVulnerabilityScanningTools

**Mitigation:**
Any of the following are enough to prevent this vulnerability for Solr servers:
Expand All @@ -32,5 +29,9 @@ Any of the following are enough to prevent this vulnerability for Solr servers:
`set SOLR_OPTS=%SOLR_OPTS% -Dlog4j2.formatMsgNoLookups=true`
* Follow any of the other mitgations listed at <https://logging.apache.org/log4j/2.x/security.html>

The Log4J security page refers to setting `log4j2.formatMsgNoLookups=true` as a "discredited" mitigation. In reality, it depends.
We've looked at the root cause and audited the code paths that lead to the vulnerability, and we feel confident in this mitigation being sufficient for Solr.
See <https://lists.apache.org/thread/kgh63sncrsm2bls884pg87mnt8vqztmz> for discussion.

**References:**
<https://logging.apache.org/log4j/2.x/security.html>