diff --git a/core/htmlsanitizer.class.inc.php b/core/htmlsanitizer.class.inc.php
index b2a7aa4c7..5bcae80eb 100644
--- a/core/htmlsanitizer.class.inc.php
+++ b/core/htmlsanitizer.class.inc.php
@@ -160,53 +160,65 @@ class HTMLDOMSanitizer extends HTMLSanitizer
 	 * @see https://www.itophub.io/wiki/page?id=2_6_0%3Aadmin%3Arich_text_limitations
 	 */
 	protected static $aTagsWhiteList = array(
-		'html' => array(),
-		'body' => array(),
 		'a' => array('href', 'name', 'style', 'target', 'title'),
-		'p' => array('style'),
-		'blockquote' => array('style'),
-		'br' => array(),
-		'span' => array('style'),
-		'div' => array('style'),
 		'b' => array(),
-		'i' => array(),
-		'u' => array(),
+		'big' => array(),
+		'blockquote' => array('style'),
+		'body' => array(),
+		'br' => array(),
+		'center' => array(),
+		'cite' => array(),
+		'code' => array('style', 'class'),
+		'del' => array(),
+		'div' => array('style'),
 		'em' => array(),
-		'strong' => array(),
-		'img' => array('src', 'style', 'alt', 'title'),
-		'ul' => array('style'),
-		'ol' => array('style'),
-		'li' => array('style'),
+		'fieldset' => array('style'),
+		'font' => array('face', 'color', 'style', 'size'),
 		'h1' => array('style'),
 		'h2' => array('style'),
 		'h3' => array('style'),
 		'h4' => array('style'),
+		'hr' => array('style'),
+		'html' => array(),
+		'i' => array(),
+		'img' => array('src', 'style', 'alt', 'title'),
+		'ins' => array(),
+		'kbd' => array(),
+		'legend' => array('style'),
+		'li' => array('style'),
 		'nav' => array('style'),
+		'ol' => array('style'),
+		'p' => array('style'),
+		'pre' => array(),
+		'q' => array(),
+		'samp' => array(),
+		's' => array(), // strikethrough
 		'section' => array('style'),
-		'code' => array('style', 'class'),
+		'small' => array(),
+		'span' => array('style'),
+		'strong' => array(),
 		'table' => array('style', 'width', 'summary', 'align', 'border', 'cellpadding', 'cellspacing'),
-		'thead' => array('style'),
 		'tbody' => array('style'),
-		'tr' => array('style', 'colspan', 'rowspan'),
 		'td' => array('style', 'colspan', 'rowspan'),
 		'th' => array('style', 'colspan', 'rowspan'),
-		'fieldset' => array('style'),
-		'legend' => array('style'),
-		'font' => array('face', 'color', 'style', 'size'),
-		'big' => array(),
-		'small' => array(),
+		'thead' => array('style'),
+		'tr' => array('style', 'colspan', 'rowspan'),
 		'tt' => array(),
-		'kbd' => array(),
-		'samp' => array(),
+		'u' => array(),
+		'ul' => array('style'),
 		'var' => array(),
-		'del' => array(),
-		's' => array(), // strikethrough
-		'ins' => array(),
-		'cite' => array(),
-		'q' => array(),
-		'hr' => array('style'),
-		'pre' => array(),
-		'center' => array(),
+	);
+
+	protected static $aTagsContentRemovableList = array(
+		'applet',
+		'basefont',
+		'canvas',
+		'code',
+		'dialog',
+		'embed',
+		'object',
+		'script',
+		'style',
 	);
 
 	protected static $aAttrsWhiteList = array(
@@ -302,6 +314,108 @@ class HTMLDOMSanitizer extends HTMLSanitizer
 	}
 	
 	protected function CleanNode(DOMNode $oElement)
+	{
+		$this->CleanNodeRemoveForbiddenTags($oElement);
+		$this->CleanNodeHandleImages($oElement);
+		$this->CleanNodeRemoveForbiddenAttributes($oElement);
+	}
+
+	protected function CleanNodeRemoveForbiddenTags(DOMNode $oElement)
+	{
+		if ($oElement->hasChildNodes())
+		{
+			$aValidatedNodes = array();
+			do
+			{
+				$bChildRemoved = false;
+
+				$aNodes = array();
+				foreach($oElement->childNodes as $oNode)
+				{
+					$aNodes[] = $oNode;
+				}
+
+				foreach($aNodes as $oNode)
+				{
+					if (($oNode instanceof DOMElement) && (!array_key_exists(strtolower($oNode->tagName), self::$aTagsWhiteList)))
+					{
+						$bChildRemoved = true;
+						$this->SmartRemoveChild($oElement, $oNode);
+					}
+					else if ($oNode instanceof DOMComment)
+					{
+						$oElement->removeChild($oNode);
+					}
+					else
+					{
+						//if the node is kept, we can recurse into it, bu we want to perform this only once (see the do/while above?)
+						$bAlreadyValidated = false;
+						/** @var \DOMNode $oValidatedNode */
+						foreach ($aValidatedNodes as $oValidatedNode)
+						{
+							if ($oValidatedNode->isSameNode($oNode))
+							{
+								$bAlreadyValidated = true;
+								break;
+							}
+						}
+						if (! $bAlreadyValidated)
+						{
+							$this->CleanNodeRemoveForbiddenTags($oNode);
+							$aValidatedNodes[] = $oNode;
+						}
+					}
+				}
+			} while ($bChildRemoved);
+		}
+	}
+
+	/**
+	 * Remove a node, but move its inner nodes in the parent.
+	 * Note: invalid/forbidden tags may be moved up, so they have to be checked again.
+	 *
+	 * @param \DOMNode $oParent
+	 * @param \DOMElement $oRemovable
+	 */
+	private function SmartRemoveChild(DOMNode $oParent, DOMElement $oRemovable)
+	{
+		if (!$oRemovable->hasChildNodes())
+		{
+			$oParent->removeChild($oRemovable);
+		}
+		else if (in_array(strtolower($oRemovable->tagName), self::$aTagsContentRemovableList))
+		{
+			$oParent->removeChild($oRemovable);
+		}
+		else
+		{
+			/** @var \DOMNode $oNode */
+			foreach ($oRemovable->childNodes as $oNode)
+			{
+				$oNode = $oNode->cloneNode(true);
+				$oParent->insertBefore($oNode, $oRemovable);
+			}
+
+			$oParent->removeChild($oRemovable);
+		}
+	}
+
+	protected function CleanNodeHandleImages(DOMNode $oElement)
+	{
+		if ($oElement->hasChildNodes())
+		{
+			foreach($oElement->childNodes as $oNode)
+			{
+				$this->CleanNodeHandleImages($oNode);
+				if (($oNode instanceof DOMElement) && (strtolower($oNode->tagName) == 'img'))
+				{
+					InlineImage::ProcessImageTag($oNode);
+				}
+			}
+		}
+	}
+
+	protected function CleanNodeRemoveForbiddenAttributes(DOMNode $oElement)
 	{
 		$aAttrToRemove = array();
 		// Gather the attributes to remove
@@ -341,35 +455,12 @@ class HTMLDOMSanitizer extends HTMLSanitizer
 				$oElement->removeAttribute($sName);
 			}
 		}
-		
+
 		if ($oElement->hasChildNodes())
 		{
-			$aChildElementsToRemove = array();
-			// Gather the child noes to remove
 			foreach($oElement->childNodes as $oNode)
 			{
-				if (($oNode instanceof DOMElement) && (!array_key_exists(strtolower($oNode->tagName), self::$aTagsWhiteList)))
-				{
-					$aChildElementsToRemove[] = $oNode;
-				}
-				else if ($oNode instanceof DOMComment)
-				{
-					$aChildElementsToRemove[] = $oNode;
-				}
-				else
-				{
-					// Recurse
-					$this->CleanNode($oNode);
-					if (($oNode instanceof DOMElement) && (strtolower($oNode->tagName) == 'img'))
-					{
-						InlineImage::ProcessImageTag($oNode);
-					}
-				}
-			}
-			// Now remove them
-			foreach($aChildElementsToRemove as $oDomElement)
-			{
-				$oElement->removeChild($oDomElement);
+				$this->CleanNodeRemoveForbiddenAttributes($oNode);
 			}
 		}
 	}
diff --git a/test/core/HTMLDOMSanitizerTest.php b/test/core/HTMLDOMSanitizerTest.php
index 004b1cc74..d20656494 100644
--- a/test/core/HTMLDOMSanitizerTest.php
+++ b/test/core/HTMLDOMSanitizerTest.php
@@ -168,6 +168,83 @@ class HTMLDOMSanitizerTest extends ItopTestCase
 		return $aTestCaseArray;
 	}
 
+	/**
+	 * Test the fix for ticket N°2556
+	 *
+	 * @dataProvider PreserveBlackListedTagContentProvider
+	 *
+	 */
+	public function testDoSanitizePreserveBlackListedTagContent($html, $expected)
+	{
+		$oSanitizer = new HTMLDOMSanitizer();
+		$sSanitizedHtml = $oSanitizer->DoSanitize($html);
+
+		$this->assertEquals($expected, str_replace("\n", '', $sSanitizedHtml));
+	}
+
+	public function PreserveBlackListedTagContentProvider()
+	{
+		return array(
+			'basic' => array(
+				'html' => '<iframe>bar</iframe>',
+				'expected' => 'bar',
+			),
+			'basic with body' => array(
+				'html' => '<body><iframe>bar</iframe></body>',
+				'expected' => 'bar',
+			),
+			'basic with html and body tags' => array(
+				'html' => '<html><body lang="EN-GB" link="#0563C1" vlink="#954F72"><iframe>bar</iframe></body></html>',
+				'expected' => 'bar',
+			),
+			'basic with attributes' => array(
+				'html' => '<iframe baz="1">bar</iframe>',
+				'expected' => 'bar',
+			),
+			'basic with comment' => array(
+				'html' => '<iframe baz="1">bar<!-- foo --></iframe>',
+				'expected' => 'bar',
+			),
+			'basic with contentRemovable tag' => array(
+				'html' => '<iframe baz="1">bar<style>foo</style><script>boo</script></iframe>',
+				'expected' => 'bar',
+			),
+			'nested' => array(
+				'html' => '<iframe>foo<article>baz</article>oof<article><iframe>bar</iframe>oof</article></iframe>',
+				'expected' => 'foobazoofbaroof',
+			),
+			'nested with not closed br' => array(
+				'html' => '<iframe>foo<article>baz</article>oof<br><article><iframe>bar</iframe>oof</article></iframe>',
+				'expected' => 'foobazoof<br>baroof',
+			),
+			'nested with allowed' => array(
+				'html' => '<iframe><div><article><p>baz</p>zab</article></div>oof</iframe>',
+				'expected' => '<div><p>baz</p>zab</div>oof',
+			),
+			'nested with spaces' => array(
+				'html' => '<iframe><article>baz</article> oof</iframe>',
+				'expected' => 'baz oof',
+			),
+			'nested with attributes' => array(
+				'html' => '<iframe baz="1"><article baz="1" biz="2">baz</article>oof</iframe>',
+				'expected' => 'bazoof',
+			),
+			'nested with allowed and attributes and spaces ' => array(
+				'html' => '<html><body><iframe baz="1"><div baz="baz"><article baz="1" biz="2">baz</article>rab</div> oof</iframe></body></html>',
+				'expected' => '<div>bazrab</div> oof',
+			),
+			'nested with allowed and contentRemovable tags' => array(
+				'html' => '<html><body><iframe baz="1"><div ><article>baz</article>rab</div> oof<embed>embedTExt</embed></iframe><style>foo</style><script>boo</script></body></html>',
+				'expected' => '<div>bazrab</div> oof',
+			),
+
+			'regression: if head present => body is not trimmed' => array(
+				'html' => '<html><head></head><body lang="EN-GB" link="#0563C1" vlink="#954F72">bar</body></html>',
+				'expected' => 'bar',
+			),
+		);
+	}
+
 	/**
 	 * Generates an appropriate value for the given attribute, or use the counter if needed.
 	 * This is necessary as most of the attributes with empty or inappropriate values (like a numeric for a href) are removed by the parser
@@ -202,5 +279,43 @@ class HTMLDOMSanitizerTest extends ItopTestCase
 
 		return true;
 	}
+
+	/**
+	 * @dataProvider CallInlineImageProcessImageTagProvider
+	 */
+	public function testDoSanitizeCallInlineImageProcessImageTag($sHtml, $iExpectedCount)
+	{
+		require_once APPROOT.'test/core/sanitizer/InlineImageMock.php';
+
+		$oSanitizer = new HTMLDOMSanitizer();
+		$oSanitizer->DoSanitize($sHtml);
+
+		$iCalledCount = \InlineImage::GetCallCounter();
+		$this->assertEquals($iExpectedCount, $iCalledCount);
+	}
+
+	public function CallInlineImageProcessImageTagProvider()
+	{
+		return array(
+			'no image' => array(
+				'html' => '<p>bar</p>',
+				'expected' => 0,
+			),
+			'basic image' => array(
+				'html' => '<img />',
+				'expected' => 1,
+			),
+			'nested images within forbidden tags' => array(
+				'html' => '<html><body><img /><iframe baz="1"><div baz="baz"><article baz="1" biz="2">baz<img /><img /></article>rab</div> oof<img /></iframe><img /></body></html>',
+				'expected' => 5,
+			),
+			'nested images within forbidden and removed tags' => array(
+				'html' => '<html><body><img /><iframe baz="1"><div baz="baz"><object baz="1" biz="2">baz<img /><img /></object>rab</div> oof<img /></iframe><img /></body></html>',
+				'expected' => 3,
+			),
+		);
+	}
+
+
 }
 
diff --git a/test/core/sanitizer/InlineImageMock.php b/test/core/sanitizer/InlineImageMock.php
new file mode 100644
index 000000000..d5ad33218
--- /dev/null
+++ b/test/core/sanitizer/InlineImageMock.php
@@ -0,0 +1,39 @@
+<?php
+/**
+ * Copyright (C) 2010-2020 Combodo SARL
+ *
+ *   This file is part of iTop.
+ *
+ *   iTop is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU Affero General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   iTop is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU Affero General Public License for more details.
+ *
+ *   You should have received a copy of the GNU Affero General Public License
+ *   along with iTop. If not, see <http: *www.gnu.org/licenses/>
+ *
+ */
+
+/**
+ * Mock class used by @see \Combodo\iTop\Test\UnitTest\Core\HTMLDOMSanitizerTest
+ *
+ */
+class InlineImage
+{
+	private static $iCallCounter = 0;
+
+	public static function ProcessImageTag(DOMNode $oNode)
+	{
+		self::$iCallCounter++;
+	}
+
+	public static function GetCallCounter()
+	{
+		return self::$iCallCounter;
+	}
+}
\ No newline at end of file