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             AUSCERT External Security Bulletin Redistribution

   CVE-2018-8026: XXE vulnerability due to Apache Solr configset upload
                                6 July 2018


        AusCERT Security Bulletin Summary

Product:           Solr
Publisher:         Apache Foundation
Operating System:  UNIX variants (UNIX, Linux, OSX)
Impact/Access:     Access Confidential Data -- Remote with User Interaction
Resolution:        Patch/Upgrade
CVE Names:         CVE-2018-8026  

Reference:         ESB-2018.1546

Original Bulletin: 

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CVE-2018-8026: XXE vulnerability due to Apache Solr configset upload
(exchange rate provider config / enum field config / TIKA parsecontext)

Severity: High

The Apache Software Foundation

Versions Affected:
Solr 6.0.0 to 6.6.4
Solr 7.0.0 to 7.3.1

The details of this vulnerability were reported by mail to the Apache
security mailing list.
This vulnerability relates to an XML external entity expansion (XXE) in Solr
config files (currency.xml, enumsConfig.xml referred from schema.xml,
TIKA parsecontext config file). In addition, Xinclude functionality provided
in these config files is also affected in a similar way. The vulnerability can
be used as XXE using file/ftp/http protocols in order to read arbitrary
local files from the Solr server or the internal network. The manipulated
files can be uploaded as configsets using Solr's API, allowing to exploit
that vulnerability. See [1] for more details.

Users are advised to upgrade to either Solr 6.6.5 or Solr 7.4.0 releases both
of which address the vulnerability. Downloads are available at [2]. Once
upgrade is complete, no other steps are required. Those releases only allow
external entities and Xincludes that refer to local files / zookeeper
resources below the Solr instance directory (using Solr's ResourceLoader);
usage of absolute URLs is denied. Keep in mind, that external entities
and XInclude are explicitly supported to better structure config files in
large installations. Before Solr 6 this was no problem, as config files were
not accessible through the APIs.

If users are unable to upgrade to Solr 6.6.5 or Solr 7.4.0 then they are
advised to make sure that Solr instances are only used locally without access
to public internet, so the vulnerability cannot be exploited. In addition,
reverse proxies should be guarded to not allow end users to reach the
configset APIs. Please refer to [3] on how to correctly secure Solr servers.

Solr 5.x and earlier are not affected by this vulnerability; those versions
do not allow to upload configsets via the API. Nevertheless, users should
upgrade those versions as soon as possible, because there may be other ways
to inject config files through file upload functionality of the old web
interface. Those versions are no longer maintained, so no deep analysis was

Yuyang Xiao, Ishan Chattopadhyaya

[1] https://issues.apache.org/jira/browse/SOLR-12450
[2] https://lucene.apache.org/solr/downloads.html
[3] https://wiki.apache.org/solr/SolrSecurity

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