diff --git a/phpBB/phpbb/textformatter/s9e/factory.php b/phpBB/phpbb/textformatter/s9e/factory.php
index e1979a27821..30a6c94fc1d 100644
--- a/phpBB/phpbb/textformatter/s9e/factory.php
+++ b/phpBB/phpbb/textformatter/s9e/factory.php
@@ -364,6 +364,12 @@ function ($m)
 		</xsl:choose>';
 		$tag->template = '<xsl:choose><xsl:when test="$S_VIEWSMILIES">' . str_replace('class="emoji"', 'class="emoji smilies"', $tag->template) . '</xsl:when><xsl:otherwise><xsl:value-of select="."/></xsl:otherwise></xsl:choose>';
 
+		// Reject shortcodes that consist of raw codepoints in hexadecimal such as ":123c:",
+		// which commonly appear as segments of IPv6 addresses
+		$tag->filterChain
+			->append(__NAMESPACE__ . '\\parser::filter_emoji')
+			->addParameterByName('tagText');
+
 		/**
 		* Modify the s9e\TextFormatter configurator after the default settings are set
 		*
diff --git a/phpBB/phpbb/textformatter/s9e/parser.php b/phpBB/phpbb/textformatter/s9e/parser.php
index 590afc0ebcf..749e11d86cf 100644
--- a/phpBB/phpbb/textformatter/s9e/parser.php
+++ b/phpBB/phpbb/textformatter/s9e/parser.php
@@ -301,6 +301,25 @@ public function set_vars(array $vars)
 		}
 	}
 
+	/**
+	* Filter an EMOJI tag to reject shortcodes that consist of raw codepoints
+	*
+	* Sequences of hexadecimal digits between colons such as ":123c:" commonly
+	* appear as segments of IPv6 addresses and should remain plain text rather
+	* than be rendered as an emoji image
+	*
+	* @param  Tag    $tag      The EMOJI tag
+	* @param  string $tag_text Original text consumed by the tag
+	* @return void
+	*/
+	static public function filter_emoji(Tag $tag, $tag_text)
+	{
+		if (preg_match('/^:[0-3][0-9a-f]{3,4}(?:-[0-9a-f]{4,5})*:$/D', $tag_text))
+		{
+			$tag->invalidate();
+		}
+	}
+
 	/**
 	* Filter a flash object's height
 	*
diff --git a/tests/text_formatter/s9e/default_formatting_test.php b/tests/text_formatter/s9e/default_formatting_test.php
index 97b04c2fb7d..2442373a907 100644
--- a/tests/text_formatter/s9e/default_formatting_test.php
+++ b/tests/text_formatter/s9e/default_formatting_test.php
@@ -320,6 +320,26 @@ function ($container)
 					$container->get('text_formatter.renderer')->set_viewsmilies(false);
 				}
 			),
+			array(
+				// PHPBB-17655 - Segments of IPv6 addresses should not be rendered as emoji
+				'IPv6: 2a09:bac3:616e:123c::1d1:f0',
+				'IPv6: 2a09:bac3:616e:123c::1d1:f0'
+			),
+			array(
+				'IPv6: 2607:fb90:ec1d:0e17:e0c6:af94:1224:28a8',
+				'IPv6: 2607:fb90:ec1d:0e17:e0c6:af94:1224:28a8'
+			),
+			array(
+				// Raw codepoint shortcodes are rejected as they cannot be told apart
+				// from segments of IPv6 addresses
+				'Codepoints: :264d: :1f600: :1234:',
+				'Codepoints: :264d: :1f600: :1234:'
+			),
+			array(
+				// Emoji shortnames keep working
+				'Shortname: :joy:',
+				'Shortname: <img alt=":joy:" class="emoji smilies" draggable="false" src="//cdn.jsdelivr.net/gh/twitter/twemoji@latest/assets/svg/1f602.svg">'
+			),
 		);
 	}
 }