CVE-2023-24813: Interpretation Conflict (CWE-436)
value: Dompdf is an HTML to PDF converter written in php. Due to the difference in the attribute parser of Dompdf and php-svg-lib, an attacker can still call arbitrary URLs with arbitrary protocols. Dompdf parses the href attribute of `image` tags and respects `xlink:href` even if `href` is specified. However, php-svg-lib, which is later used to parse the svg file, parses the href attribute. Since `href` is respected if both `xlink:href` and `href` is specified, it's possible to bypass the protection on the Dompdf side by providing an empty `xlink:href` attribute. An attacker can exploit the vulnerability to call arbitrary URLs with arbitrary protocols if they provide an SVG file to the Dompdf. In PHP versions before 8.0.0, it leads to arbitrary unserialize, which will lead, at the very least, to arbitrary file deletion and might lead to remote code execution, depending on available classes. This vulnerability has been addressed in commit `95009ea98` which has been included in release version 2.0.3. Users are advised to upgrade. There are no known workarounds for this vulnerability.
CWE description: Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.
CVSS v3 base score: 9.8
Published: 2023-02-07T19:15Z
Repository: https://github.com/dompdf/dompdf
Language: PHP
Files changed: src/Image/Cache.php
Commit date: 2023-02-07 07:43:20 -0500
Commit message: Validate both bare and namespaced SVG image HREF attributes
Diff: diff --git a/src/Image/Cache.php b/src/Image/Cache.php
index 6141cb50..8e36aa2b 100644
--- a/src/Image/Cache.php
+++ b/src/Image/Cache.php
@@ -133,19 +133,23 @@ class Cache
                 xml_set_element_handler(
                     $parser,
                     function ($parser, $name, $attributes) use ($options, $parsed_url, $full_url) {
                         if (strtolower($name) === "image") {
                             $attributes = array_change_key_case($attributes, CASE_LOWER);
-                            $url = $attributes["xlink:href"] ?? $attributes["href"];
-                            if (!empty($url)) {
-                                $inner_full_url = Helpers::build_url($parsed_url["protocol"], $parsed_url["host"], $parsed_url["path"], $url);
-                                if ($inner_full_url === $full_url) {
-                                    throw new ImageException("SVG self-reference is not allowed", E_WARNING);
-                                }
-                                [$resolved_url, $type, $message] = self::resolve_url($url, $parsed_url["protocol"], $parsed_url["host"], $parsed_url["path"], $options);
-                                if (!empty($message)) {
-                                    throw new ImageException("This SVG document references a restricted resource. $message", E_WARNING);
+                            $urls = [];
+                            $urls[] = $attributes["xlink:href"] ?? "";
+                            $urls[] = $attributes["href"] ?? "";
+                            foreach ($urls as $url) {
+                                if (!empty($url)) {
+                                    $inner_full_url = Helpers::build_url($parsed_url["protocol"], $parsed_url["host"], $parsed_url["path"], $url);
+                                    if ($inner_full_url === $full_url) {
+                                        throw new ImageException("SVG self-reference is not allowed", E_WARNING);
+                                    }
+                                    [$resolved_url, $type, $message] = self::resolve_url($url, $parsed_url["protocol"], $parsed_url["host"], $parsed_url["path"], $options);
+                                    if (!empty($message)) {
+                                        throw new ImageException("This SVG document references a restricted resource. $message", E_WARNING);
+                                    }
                                 }
                             }
                         }
                     },
                     false
@@ -154,10 +158,11 @@ class Cache
                 if (($fp = fopen($resolved_url, "r")) !== false) {
                     while ($line = fread($fp, 8192)) {
                         xml_parse($parser, $line, false);
                     }
                     fclose($fp);
+                    xml_parse($parser, "", true);
                 }
                 xml_parser_free($parser);
             }
         } catch (ImageException $e) {
             if ($tempfile) {

Vulnerable code:                             $url = $attributes["xlink:href"] ?? $attributes["href"];
                            if (!empty($url)) {
                                $inner_full_url = Helpers::build_url($parsed_url["protocol"], $parsed_url["host"], $parsed_url["path"], $url);
                                if ($inner_full_url === $full_url) {
                                    throw new ImageException("SVG self-reference is not allowed", E_WARNING);
                                }
                                [$resolved_url, $type, $message] = self::resolve_url($url, $parsed_url["protocol"], $parsed_url["host"], $parsed_url["path"], $options);
                                if (!empty($message)) {
                                    throw new ImageException("This SVG document references a restricted resource. $message", E_WARNING);
Fixed code:                             $urls = [];
                            $urls[] = $attributes["xlink:href"] ?? "";
                            $urls[] = $attributes["href"] ?? "";
                            foreach ($urls as $url) {
                                if (!empty($url)) {
                                    $inner_full_url = Helpers::build_url($parsed_url["protocol"], $parsed_url["host"], $parsed_url["path"], $url);
                                    if ($inner_full_url === $full_url) {
                                        throw new ImageException("SVG self-reference is not allowed", E_WARNING);
                                    }
                                    [$resolved_url, $type, $message] = self::resolve_url($url, $parsed_url["protocol"], $parsed_url["host"], $parsed_url["path"], $options);
                                    if (!empty($message)) {
                                        throw new ImageException("This SVG document references a restricted resource. $message", E_WARNING);
                                    }
                    xml_parse($parser, "", true);