CVE-2020-6817

First published: Mon Mar 30 2020(Updated: )

### Impact `bleach.clean` behavior parsing style attributes could result in a regular expression denial of service (ReDoS). Calls to ``bleach.clean`` with an allowed tag with an allowed ``style`` attribute are vulnerable to ReDoS. For example, ``bleach.clean(..., attributes={'a': ['style']})``. ### Patches 3.1.4 ### Workarounds * do not whitelist the style attribute in `bleach.clean` calls * limit input string length ### References * https://bugzilla.mozilla.org/show_bug.cgi?id=1623633 * https://www.regular-expressions.info/redos.html * https://blog.r2c.dev/posts/finding-python-redos-bugs-at-scale-using-dlint-and-r2c/ * https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-6817 ### Credits * Reported by schwag09 of r2c ### For more information If you have any questions or comments about this advisory: * Open an issue at https://github.com/mozilla/bleach/issues * Email us at security@mozilla.org

Credit: security@mozilla.org security@mozilla.org

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