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xml_parse() would attempt to fetch external files or URLs as needed to resolve DTD and entity references in an XML value, thus allowing unprivileged database users to attempt to fetch data with the privileges of the database server. While the external data wouldn't get returned directly to the user, portions of it could be exposed in error messages if the data didn't parse as valid XML; and in any case the mere ability to check existence of a file might be useful to an attacker. The ideal solution to this would still allow fetching of references that are listed in the host system's XML catalogs, so that documents can be validated according to installed DTDs. However, doing that with the available libxml2 APIs appears complex and error-prone, so we're not going to risk it in a security patch that necessarily hasn't gotten wide review. So this patch merely shuts off all access, causing any external fetch to silently expand to an empty string. A future patch may improve this. In HEAD and 9.2, also suppress warnings about undefined entities, which would otherwise occur as a result of not loading referenced DTDs. Previous branches don't show such warnings anyway, due to different error handling arrangements. Credit to Noah Misch for first reporting the problem, and for much work towards a solution, though this simplistic approach was not his preference. Also thanks to Daniel Veillard for consultation. Security: CVE-2012-3489 |
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