checkstyle is vulnerable to XML External Entity (XXE). The vulnerability exists because it allows loading of external DTDs as a default feature, allowing an attacker to call a malicious external DTD.
checkstyle.org/releasenotes.html#Release_8.18
github.com/checkstyle/checkstyle/issues/6474
github.com/checkstyle/checkstyle/issues/6478
github.com/checkstyle/checkstyle/pull/6476
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