From 9f8edb7f326c6fb5bd090c80411e9f822c99a4dc Mon Sep 17 00:00:00 2001
From: ed <s@ocv.me>
Date: Sat, 26 Aug 2023 17:37:02 +0000
Subject: [PATCH] make markdown slightly safer without the nohtml volflag by
 running dompurify after marked.parse if plugins are not enabled; adds no
 protection against the more practical approach of just putting a malicious
 <script> in an html file and uploading that, but one footgun less is one less
 footgun

---
 README.md                      | 1 +
 copyparty/web/browser.js       | 7 ++++++-
 copyparty/web/md.js            | 2 ++
 scripts/deps-docker/Dockerfile | 8 ++++++++
 4 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index d867ceff..904624ee 100644
--- a/README.md
+++ b/README.md
@@ -1599,6 +1599,7 @@ some notes on hardening
 * set `--rproxy 0` if your copyparty is directly facing the internet (not through a reverse-proxy)
   * cors doesn't work right otherwise
 * if you allow anonymous uploads or otherwise don't trust the contents of a volume, you can prevent XSS with volflag `nohtml`
+  * this returns html documents as plaintext, and also disables markdown rendering
 
 safety profiles:
 
diff --git a/copyparty/web/browser.js b/copyparty/web/browser.js
index 26778b9e..f3458dce 100644
--- a/copyparty/web/browser.js
+++ b/copyparty/web/browser.js
@@ -7123,7 +7123,12 @@ function show_md(md, name, div, url, depth) {
 
 	try {
 		clmod(div, 'mdo', 1);
-		if (sandbox(div, sb_md, 'mdo', marked.parse(md, marked_opts)))
+
+		var md_html = marked.parse(md, marked_opts);
+		if (!have_emp)
+			md_html = DOMPurify.sanitize(md_html);
+
+		if (sandbox(div, sb_md, 'mdo', md_html))
 			return;
 
 		ext = md_plug.post;
diff --git a/copyparty/web/md.js b/copyparty/web/md.js
index 5e06f413..3d20105c 100644
--- a/copyparty/web/md.js
+++ b/copyparty/web/md.js
@@ -212,6 +212,8 @@ function convert_markdown(md_text, dest_dom) {
 
     try {
         var md_html = marked.parse(md_text, marked_opts);
+        if (!have_emp)
+            md_html = DOMPurify.sanitize(md_html);
     }
     catch (ex) {
         if (ext)
diff --git a/scripts/deps-docker/Dockerfile b/scripts/deps-docker/Dockerfile
index cccdad46..95a2e177 100644
--- a/scripts/deps-docker/Dockerfile
+++ b/scripts/deps-docker/Dockerfile
@@ -3,6 +3,7 @@ WORKDIR /z
 ENV     ver_asmcrypto=c72492f4a66e17a0e5dd8ad7874de354f3ccdaa5 \
         ver_hashwasm=4.9.0 \
         ver_marked=4.3.0 \
+        ver_dompf=3.0.5 \
         ver_mde=2.18.0 \
         ver_codemirror=5.65.12 \
         ver_fontawesome=5.13.0 \
@@ -13,6 +14,7 @@ ENV     ver_asmcrypto=c72492f4a66e17a0e5dd8ad7874de354f3ccdaa5 \
 # https://github.com/markedjs/marked/releases
 # https://github.com/Ionaru/easy-markdown-editor/tags
 # https://github.com/codemirror/codemirror5/releases
+# https://github.com/cure53/DOMPurify/releases
 # https://github.com/Daninet/hash-wasm/releases
 # https://github.com/openpgpjs/asmcrypto.js
 # https://github.com/google/zopfli/tags
@@ -27,6 +29,7 @@ RUN     mkdir -p /z/dist/no-pk \
         && wget https://github.com/markedjs/marked/archive/v$ver_marked.tar.gz -O marked.tgz \
         && wget https://github.com/Ionaru/easy-markdown-editor/archive/$ver_mde.tar.gz -O mde.tgz \
         && wget https://github.com/codemirror/codemirror5/archive/$ver_codemirror.tar.gz -O codemirror.tgz \
+        && wget https://github.com/cure53/DOMPurify/archive/refs/tags/$ver_dompf.tar.gz -O dompurify.tgz \
         && wget https://github.com/FortAwesome/Font-Awesome/releases/download/$ver_fontawesome/fontawesome-free-$ver_fontawesome-web.zip -O fontawesome.zip \
         && wget https://github.com/google/zopfli/archive/zopfli-$ver_zopfli.tar.gz -O zopfli.tgz \
         && wget https://github.com/Daninet/hash-wasm/releases/download/v$ver_hashwasm/hash-wasm@$ver_hashwasm.zip -O hash-wasm.zip \
@@ -48,6 +51,7 @@ RUN     mkdir -p /z/dist/no-pk \
             && cd easy-markdown-editor* \
             && npm install \
             && npm i gulp-cli -g ) \
+        && tar -xf dompurify.tgz \
         && tar -xf prism.tgz \
         && unzip fontawesome.zip \
         && tar -xf zopfli.tgz
@@ -120,6 +124,10 @@ RUN     cd easy-markdown-editor-$ver_mde \
         && cp -pv dist/easymde.min.js /z/dist/easymde.js
 
 
+# build dompurify
+RUN     (echo; cat DOMPurify-$ver_dompf/dist/purify.min.js) >> /z/dist/marked.js
+
+
 # build fontawesome and scp
 COPY    mini-fa.sh /z
 COPY    mini-fa.css /z