[CVE-2020-13957] The checks added to unauthenticated configset uploads in Apache Solr can be circumvented

Severity: High

Vendor: The Apache Software Foundation

Versions Affected:
6.6.0 to 6.6.5
7.0.0 to 7.7.3
8.0.0 to 8.6.2

Description:
Solr prevents some features considered dangerous (which could be used for
remote code execution) to be configured in a ConfigSet that's uploaded via
API without authentication/authorization. The checks in place to prevent
such features can be circumvented by using a combination of UPLOAD/CREATE
actions.

Mitigation:
Any of the following are enough to prevent this vulnerability:
* Disable UPLOAD command in ConfigSets API if not used by setting the
system property: "configset.upload.enabled" to "false" [1]
* Use Authentication/Authorization and make sure unknown requests aren't
allowed [2]
* Upgrade to Solr 8.6.3 or greater.
* If upgrading is not an option, consider applying the patch in SOLR-14663
([3])
* No Solr API, including the Admin UI, is designed to be exposed to
non-trusted parties. Tune your firewall so that only trusted computers and
people are allowed access

Credit:
Tomás Fernández Löbbe, András Salamon

References:
[1] https://lucene.apache.org/solr/guide/8_6/configsets-api.html
[2]
https://lucene.apache.org/solr/guide/8_6/authentication-and-authorization-plugins.html
[3] https://issues.apache.org/jira/browse/SOLR-14663
[4] https://issues.apache.org/jira/browse/SOLR-14925
[5] https://wiki.apache.org/solr/SolrSecurity