REXML is an XML toolkit for Ruby. The REXML gem before 3.3.9 has a ReDoS vulnerability when it parses an XML that has many digits between &# and x...; in a hex numeric character reference (&#x...;). This does not happen with Ruby 3.2 or later. Ruby 3.1 is the only affected maintained Ruby. The REXML gem 3.3.9 or later include the patch to fix the vulnerability.
A flaw was found in the REXML XML toolkit for Ruby. Parsing XML data containing a large number of digits between `&# `and `x...;` in a hex numeric character reference (`&#x...;`) can trigger a regular expression denial of service (ReDoS) condition, leading to a denial of service.
USN-7091-1 fixed several vulnerabilities in Ruby. This update provides the corresponding update for ruby2.7 in Ubuntu 20.04 LTS. It was discovered that Ruby incorrectly handled parsing of an XML document that has specific XML characters in an attribute value using REXML gem. An attacker could use this issue to cause Ruby to crash, resulting in a denial of service. This issue only affected in Ubuntu 22.04 LTS and Ubuntu 24.04 LTS. It was discovered that Ruby incorrectly handled parsing of an XML document that has many entity expansions with SAX2 or pull parser API. An attacker could use this issue to cause Ruby to crash, resulting in a denial of service. It was discovered that Ruby incorrectly handled parsing of an XML document that has many digits in a hex numeric character reference. An attacker could use this issue to cause Ruby to crash, resulting in a denial of service.
