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Reference.org
Double encoding
open-in-new
<p>Double encoding is the act of encoding data twice in a row using the same encoding scheme. It is usually used as an attack technique to bypass <a href="/facts/Authorization/FYFAkCH2">authorization</a> schemes or security filters that intercept user input. In double encoding attacks against security filters, characters of the payload that are treated as illegal by those filters are replaced with their double-encoded form. </p><p>Double URI-encoding is a special type of double encoding in which data is <a href="/facts/Percent-encoding/zprLw5se">URI-encoded</a> twice in a row. It has been used to bypass authorization schemes and security filters against <a href="/facts/Code_injection/6gPRDpd1">code injection</a>, <a href="/facts/Directory_traversal_attack/eLfodPKd">directory traversal</a>, <a href="/facts/Cross-site_scripting/dhtusKKm">cross-site scripting</a> (XSS) and <a href="/facts/SQL_injection/QD0cwbk5">SQL injection</a>. </p>