diff --git a/src/wp-includes/kses.php b/src/wp-includes/kses.php
index 18f183cf3dd19..e4bf6b4e941c3 100644
--- a/src/wp-includes/kses.php
+++ b/src/wp-includes/kses.php
@@ -206,8 +206,10 @@
 			'longdesc' => true,
 			'vspace'   => true,
 			'src'      => true,
+			'srcset'   => true,
 			'usemap'   => true,
 			'width'    => true,
+			'sizes'    => true,
 		),
 		'ins'        => array(
 			'datetime' => true,
@@ -250,6 +252,7 @@
 		'p'          => array(
 			'align' => true,
 		),
+		'picture'    => array(),
 		'pre'        => array(
 			'width' => true,
 		),
@@ -270,6 +273,12 @@
 			'align' => true,
 		),
 		'small'      => array(),
+		'source'     => array(
+			'srcset' => true,
+			'type'   => true,
+			'media'  => true,
+			'sizes'  => true,
+		),
 		'strike'     => array(),
 		'strong'     => array(),
 		'sub'        => array(),
@@ -768,7 +777,6 @@ function wp_kses( $content, $allowed_html, $allowed_protocols = array() ) {
  * @return string Filtered attribute.
  */
 function wp_kses_one_attr( $attr, $element ) {
-	$uris              = wp_kses_uri_attributes();
 	$allowed_html      = wp_kses_allowed_html( 'post' );
 	$allowed_protocols = wp_allowed_protocols();
 	$attr              = wp_kses_no_null( $attr, array( 'slash_zero' => 'keep' ) );
@@ -812,10 +820,7 @@ function wp_kses_one_attr( $attr, $element ) {
 		// Sanitize quotes, angle braces, and entities.
 		$value = esc_attr( $value );
 
-		// Sanitize URI values.
-		if ( in_array( strtolower( $name ), $uris, true ) ) {
-			$value = wp_kses_bad_protocol( $value, $allowed_protocols );
-		}
+		$value = wp_kses_sanitize_uris( $name, $value, $allowed_protocols );
 
 		$attr  = "$name=$quote$value$quote";
 		$vless = 'n';
@@ -1034,6 +1039,7 @@ function wp_kses_uri_attributes() {
 		'src',
 		'usemap',
 		'xmlns',
+		'srcset',
 	);
 
 	/**
@@ -1394,7 +1400,6 @@ function wp_kses_hair( $attr, $allowed_protocols ) {
 	$attrarr  = array();
 	$mode     = 0;
 	$attrname = '';
-	$uris     = wp_kses_uri_attributes();
 
 	// Loop through the whole attribute list.
 
@@ -1442,9 +1447,9 @@ function wp_kses_hair( $attr, $allowed_protocols ) {
 				if ( preg_match( '%^"([^"]*)"(\s+|/?$)%', $attr, $match ) ) {
 					// "value"
 					$thisval = $match[1];
-					if ( in_array( strtolower( $attrname ), $uris, true ) ) {
-						$thisval = wp_kses_bad_protocol( $thisval, $allowed_protocols );
-					}
+
+					// Sanitize URI values.
+					$thisval = wp_kses_sanitize_uris( $attrname, $thisval, $allowed_protocols );
 
 					if ( false === array_key_exists( $attrname, $attrarr ) ) {
 						$attrarr[ $attrname ] = array(
@@ -1464,9 +1469,8 @@ function wp_kses_hair( $attr, $allowed_protocols ) {
 				if ( preg_match( "%^'([^']*)'(\s+|/?$)%", $attr, $match ) ) {
 					// 'value'
 					$thisval = $match[1];
-					if ( in_array( strtolower( $attrname ), $uris, true ) ) {
-						$thisval = wp_kses_bad_protocol( $thisval, $allowed_protocols );
-					}
+					// Sanitize URI values.
+					$thisval = wp_kses_sanitize_uris( $attrname, $thisval, $allowed_protocols );
 
 					if ( false === array_key_exists( $attrname, $attrarr ) ) {
 						$attrarr[ $attrname ] = array(
@@ -1486,9 +1490,8 @@ function wp_kses_hair( $attr, $allowed_protocols ) {
 				if ( preg_match( "%^([^\s\"']+)(\s+|/?$)%", $attr, $match ) ) {
 					// value
 					$thisval = $match[1];
-					if ( in_array( strtolower( $attrname ), $uris, true ) ) {
-						$thisval = wp_kses_bad_protocol( $thisval, $allowed_protocols );
-					}
+					// Sanitize URI values.
+					$thisval = wp_kses_sanitize_uris( $attrname, $thisval, $allowed_protocols );
 
 					if ( false === array_key_exists( $attrname, $attrarr ) ) {
 						$attrarr[ $attrname ] = array(
@@ -1530,6 +1533,42 @@ function wp_kses_hair( $attr, $allowed_protocols ) {
 	return $attrarr;
 }
 
+/**
+ * Sanitizes URI values in HTML attributes.
+ *
+ * This function centralizes logic for cleaning attribute values that are expected to contain URLs.
+ * It checks if the attribute name is one that should contain a URI (e.g., 'href', 'src', 'srcset').
+ * For attributes that can contain multiple URIs (such as 'srcset'), it splits the value and sanitizes each URI individually.
+ * All URI values are passed through {@see wp_kses_bad_protocol()} to remove disallowed protocols (e.g., 'javascript:').
+ *
+ * @since 6.9.0
+ *
+ * @param string   $attrname          The attribute name to test.
+ * @param string   $attrvalue         The attribute value to sanitize.
+ * @param string[] $allowed_protocols Array of allowed URL protocols.
+ * @param string[] $multi_uri         Optional. Attributes that can contain multiple URIs. Default is array( 'srcset' ).
+ * @return string Sanitized attribute value.
+ */
+function wp_kses_sanitize_uris( $attrname, $attrvalue, $allowed_protocols, $multi_uri = array( 'srcset' ) ) {
+	$uris = wp_kses_uri_attributes();
+
+	if ( ! in_array( strtolower( $attrname ), $uris, true ) ) {
+		return $attrvalue;
+	} else {
+		if ( in_array( strtolower( $attrname ), $multi_uri, true ) ) {
+			$thesevals = preg_split( '/\s*,\s*/', $attrvalue );
+		} else {
+			$thesevals = array( $attrvalue );
+		}
+	}
+
+	foreach ( (array) $thesevals as $key => $val ) {
+		$thesevals[ $key ] = wp_kses_bad_protocol( $val, $allowed_protocols );
+	}
+
+	return implode( ', ', $thesevals );
+}
+
 /**
  * Finds all attributes of an HTML element.
  *
diff --git a/tests/phpunit/tests/kses.php b/tests/phpunit/tests/kses.php
index 3384a6f137e81..7bbfda211b469 100644
--- a/tests/phpunit/tests/kses.php
+++ b/tests/phpunit/tests/kses.php
@@ -2394,4 +2394,240 @@ public function data_allowed_attributes_in_descriptions() {
 			),
 		);
 	}
+
+	/**
+	 * Test that wp_filter_post_kses() filters img tags correctly and allows the srcset element.
+	 *
+	 * @ticket 29807
+	 */
+	public function test_wp_filter_post_kses_img() {
+		global $allowedposttags;
+
+		$attributes = array(
+			'class'    => 'classname',
+			'id'       => 'idattr',
+			'style'    => 'color: red;',
+			'alt'      => 'alt',
+			'src'      => '/test.png',
+			'srcset'   => '/test.png 1x, /test-2x.png 2x, /test-3x.png',
+			'width'    => '100',
+			'height'   => '100',
+			'usemap'   => '#hash',
+			'vspace'   => '20',
+			'hspace'   => '20',
+			'longdesc' => 'this is the longdesc',
+			'align'    => 'middle',
+			'border'   => '5',
+			'sizes'    => '(max-width: 600px) 100vw, 50vw',
+		);
+
+		foreach ( $attributes as $name => $value ) {
+			if ( $name === $value ) {
+				$string        = "<img $value />";
+				$expect_string = '<img ' . trim( $value, ';' ) . ' />';
+			} else {
+				$string        = "<img $name='$value' />";
+				$expect_string = "<img $name='" . trim( $value, ';' ) . "' />";
+			}
+
+			$this->assertEquals( $expect_string, wp_kses( $string, $allowedposttags ) );
+		}
+	}
+
+	/**
+	 * @ticket 29807
+	 *
+	 * @param string $unfiltered Unfiltered srcset value before wp_kses.
+	 * @param string $expected   Expected srcset value after wp_kses.
+	 *
+	 * @dataProvider data_wp_kses_srcset
+	 */
+	public function test_wp_kses_srcset( $unfiltered, $expected ) {
+		$unfiltered = "<img src='test.png' srcset='{$unfiltered}' />";
+		$expected   = "<img src='test.png' srcset='{$expected}' />";
+		$this->assertEquals( $expected, wp_kses_post( $unfiltered ) );
+	}
+
+	public function data_wp_kses_srcset() {
+		return array(
+			array(
+				'/test.png 1x, /test-2x.png 2x',
+				'/test.png 1x, /test-2x.png 2x',
+			),
+			array(
+				'bad://localhost/test.png 1x, http://localhost/test-2x.png 2x',
+				'//localhost/test.png 1x, http://localhost/test-2x.png 2x',
+			),
+			array(
+				'http://localhost/test.png 1x, bad://localhost/test-2x.png 2x',
+				'http://localhost/test.png 1x, //localhost/test-2x.png 2x',
+			),
+			array(
+				'http://localhost/test.png,big 1x, bad://localhost/test.png,medium 2x',
+				'http://localhost/test.png, big 1x, //localhost/test.png, medium 2x',
+			),
+			array(
+				'path/to/test.png 1x, path/to/test-2x.png 2x',
+				'path/to/test.png 1x, path/to/test-2x.png 2x',
+			),
+		);
+	}
+
+	/**
+	 * @ticket 29807
+	 */
+	public function test_wp_filter_post_kses_picture() {
+		global $allowedposttags;
+
+		$html = '<picture><source srcset="pear-mobile.jpeg" media="(max-width: 720px)" type="image/png"><source srcset="pear-tablet.jpeg" media="(max-width: 1280px)" type="image/png"><img src="pear-desktop.jpeg" alt="The pear is juicy."></picture>';
+		$this->assertEquals( $html, wp_kses( $html, $allowedposttags ) );
+
+		$html = '<picture><source srcset="https://wordpress.org/pear-mobile.jpeg" media="(max-width: 720px)" type="image/png"><source srcset="https://wordpress.org/pear-tablet.jpeg 500w, https://wordpress.org/pear-tablet.jpeg" media="(max-width: 1280px)" type="image/png"><img src="pear-desktop.jpeg" alt="The pear is juicy."></picture>';
+		$this->assertEquals( $html, wp_kses( $html, $allowedposttags ) );
+
+		// Test bad protocol in srcset
+		$original = '<picture><source srcset="bad://pear-mobile.jpeg" media="(max-width: 720px)" type="image/png"><source srcset="pear-tablet.jpeg" media="(max-width: 1280px)" type="image/png"><img src="pear-desktop.jpeg" alt="The pear is juicy."></picture>';
+		$expected = '<picture><source srcset="//pear-mobile.jpeg" media="(max-width: 720px)" type="image/png"><source srcset="pear-tablet.jpeg" media="(max-width: 1280px)" type="image/png"><img src="pear-desktop.jpeg" alt="The pear is juicy."></picture>';
+		$this->assertEquals( $expected, wp_kses( $original, $allowedposttags ) );
+	}
+
+	/**
+	 * Test wp_kses_sanitize_uris function directly.
+	 *
+	 * @ticket 29807
+	 * @dataProvider data_wp_kses_sanitize_uris
+	 */
+	public function test_wp_kses_sanitize_uris( $attrname, $attrvalue, $expected, $multi_uri = array( 'srcset' ) ) {
+		$allowed_protocols = wp_allowed_protocols();
+		$result            = wp_kses_sanitize_uris( $attrname, $attrvalue, $allowed_protocols, $multi_uri );
+		$this->assertEquals( $expected, $result );
+	}
+
+	public function data_wp_kses_sanitize_uris() {
+		return array(
+			// Test non-URI attribute.
+			array( 'alt', 'description', 'description' ),
+
+			// Test single URI attribute.
+			array( 'src', 'http://example.com/image.jpg', 'http://example.com/image.jpg' ),
+
+			// Test single URI with bad protocol.
+			array( 'src', 'javascript:alert(1)', 'alert(1)' ),
+
+			// Test srcset with multiple URIs.
+			array( 'srcset', 'image1.jpg 1x, image2.jpg 2x', 'image1.jpg 1x, image2.jpg 2x' ),
+
+			// Test srcset with bad protocol.
+			array( 'srcset', 'javascript:alert(1) 1x, http://example.com/image.jpg 2x', 'alert(1) 1x, http://example.com/image.jpg 2x' ),
+
+			// Test custom multi_uri parameter.
+			array( 'custom', 'url1.jpg, url2.jpg', 'url1.jpg, url2.jpg', array( 'custom' ) ),
+		);
+	}
+
+	/**
+	 * Test edge cases for srcset sanitization.
+	 *
+	 * @ticket 29807
+	 * @dataProvider data_wp_kses_srcset_edge_cases
+	 */
+	public function test_wp_kses_srcset_edge_cases( $srcset_value, $expected ) {
+		$allowed_protocols = wp_allowed_protocols();
+		$result            = wp_kses_sanitize_uris( 'srcset', $srcset_value, $allowed_protocols );
+		$this->assertEquals( $expected, $result );
+	}
+
+	public function data_wp_kses_srcset_edge_cases() {
+		return array(
+			// Test an empty srcset.
+			array( '', '' ),
+
+			// Srcset with extra whitespace.
+			array( '  image1.jpg 1x  ,   image2.jpg 2x  ', '  image1.jpg 1x, image2.jpg 2x  ' ),
+
+			// Srcset with single URL and no descriptor.
+			array( 'image.jpg', 'image.jpg' ),
+
+			// Srcset with complex descriptors.
+			array( 'small.jpg 480w, medium.jpg 800w, large.jpg 1200w', 'small.jpg 480w, medium.jpg 800w, large.jpg 1200w' ),
+		);
+	}
+
+	/**
+	 * Test malicious input sanitization in srcset.
+	 *
+	 * @ticket 29807
+	 */
+	public function test_wp_kses_malicious_input() {
+		global $allowedposttags;
+
+		// JavaScript in srcset - the entire img tag gets escaped when it contains dangerous content.
+		$original = '<img srcset="javascript:alert(1) 1x, data:text/html,<script>alert(1)</script> 2x" />';
+		$result   = wp_kses( $original, $allowedposttags );
+		// The whole img tag should be escaped when it contains script content.
+		$this->assertStringStartsWith( '&lt;', $result );
+
+		// Script tag in picture element (should be stripped).
+		$original = '<picture><script>alert(1)</script><source srcset="image.jpg"><img src="fallback.jpg"></picture>';
+		$result   = wp_kses( $original, $allowedposttags );
+		// Script content should be converted to text, not completely removed.
+		$this->assertStringContainsString( 'alert(1)', $result );
+		$this->assertStringNotContainsString( '<script>', $result );
+
+		// Onclick in source element (should be stripped)
+		$original = '<picture><source srcset="image.jpg" onclick="alert(1)"><img src="fallback.jpg"></picture>';
+		$expected = '<picture><source srcset="image.jpg"><img src="fallback.jpg"></picture>';
+		$this->assertEquals( $expected, wp_kses( $original, $allowedposttags ) );
+	}
+
+	/**
+	 * Test sizes attribute handling.
+	 *
+	 * @ticket 29807
+	 */
+	public function test_wp_kses_sizes_attribute() {
+		global $allowedposttags;
+
+		// Valid sizes attribute.
+		$html = '<img src="image.jpg" sizes="(max-width: 600px) 100vw, 50vw" />';
+		$this->assertEquals( $html, wp_kses( $html, $allowedposttags ) );
+
+		// Complex sizes with multiple conditions.
+		$html = '<img src="image.jpg" sizes="(max-width: 320px) 280px, (max-width: 640px) 580px, 800px" />';
+		$this->assertEquals( $html, wp_kses( $html, $allowedposttags ) );
+
+		// Sizes in source element.
+		$html = '<picture><source srcset="mobile.jpg" sizes="100vw" media="(max-width: 600px)"><img src="desktop.jpg"></picture>';
+		$this->assertEquals( $html, wp_kses( $html, $allowedposttags ) );
+	}
+
+	/**
+	 * Test comprehensive responsive image scenarios.
+	 *
+	 * @ticket 29807
+	 */
+	public function test_wp_kses_comprehensive_responsive_images() {
+		global $allowedposttags;
+
+		// Test complex srcset with width descriptors.
+		$html = '<img src="default.jpg" srcset="small.jpg 480w, medium.jpg 768w, large.jpg 1024w, xlarge.jpg 1440w" sizes="(max-width: 480px) 100vw, (max-width: 768px) 75vw, 50vw" alt="Responsive image" />';
+		$this->assertEquals( $html, wp_kses( $html, $allowedposttags ) );
+
+		// Test picture with multiple sources and mixed protocols.
+		$original = '<picture><source srcset="javascript:void(0) 480w, https://example.com/mobile.webp 480w" type="image/webp" media="(max-width: 600px)"><source srcset="bad://example.com/tablet.jpg 768w, https://example.com/tablet.jpg 768w" type="image/jpeg" media="(max-width: 1200px)"><img src="https://example.com/desktop.jpg" alt="Picture element test" /></picture>';
+		$result   = wp_kses( $original, $allowedposttags );
+
+		// Should remove bad protocols but keep valid ones.
+		$this->assertStringContainsString( 'https://example.com/mobile.webp', $result );
+		$this->assertStringContainsString( 'https://example.com/tablet.jpg', $result );
+		$this->assertStringNotContainsString( 'javascript:', $result );
+		$this->assertStringNotContainsString( 'bad://', $result );
+
+		// Test nested picture scenario.
+		$original = '<picture><picture><source srcset="inner.jpg"></picture><source srcset="outer.jpg"><img src="fallback.jpg"></picture>';
+		$result   = wp_kses( $original, $allowedposttags );
+		// KSES allows the nesting but should preserve the structure.
+		$this->assertStringContainsString( '<picture>', $result );
+		$this->assertStringContainsString( '<source', $result );
+	}
 }