From 42af4cd890cef9a9c37b191368789f5383797cfe Mon Sep 17 00:00:00 2001
From: Max Burri <burri@puzzle.ch>
Date: Wed, 8 Jul 2026 13:47:21 +0000
Subject: [PATCH 1/4] chore: harden markdown renderer sanitization

---
 app/components/markdown.tsx | 43 +++++++++++++++++++++++++++++++++----
 1 file changed, 39 insertions(+), 4 deletions(-)

diff --git a/app/components/markdown.tsx b/app/components/markdown.tsx
index c99a39682..f69e4a954 100644
--- a/app/components/markdown.tsx
+++ b/app/components/markdown.tsx
@@ -1,13 +1,46 @@
 import clsx from "clsx";
 import { ComponentProps } from "react";
 import ReactMarkdown from "react-markdown";
-import rehypeRaw from "rehype-raw";
-import rehypeSanitize from "rehype-sanitize";
+import rehypeSanitize, { defaultSchema } from "rehype-sanitize";
 import remarkGfm from "remark-gfm";
 
 import classes from "@/components/markdown.module.css";
 import { palette } from "@/themes/palette";
 
+const sanitizeSchema = {
+  ...defaultSchema,
+  tagNames: [
+    "h1",
+    "h2",
+    "h3",
+    "h4",
+    "h5",
+    "h6",
+    "p",
+    "strong",
+    "em",
+    "ins",
+    "del",
+    "s",
+    "ul",
+    "ol",
+    "li",
+    "blockquote",
+    "code",
+    "pre",
+    "br",
+    "hr",
+    "a",
+  ],
+  attributes: {
+    ...defaultSchema.attributes,
+    a: ["href", "title", "target"],
+    "*": (defaultSchema.attributes?.["*"] ?? []).filter(
+      (attr) => !(typeof attr === "string" && attr.startsWith("on"))
+    ),
+  },
+};
+
 const components: ComponentProps<typeof ReactMarkdown>["components"] = {
   h1: ({ children, className, ...props }) => (
     <h1 className={clsx(className, classes.common)} {...props}>
@@ -47,6 +80,7 @@ const components: ComponentProps<typeof ReactMarkdown>["components"] = {
   a: ({ children, className, style, ...props }) => (
     <a
       target="_blank"
+      rel="noopener noreferrer"
       className={clsx(className, classes.common)}
       style={{ ...style, color: palette.primary.main }}
       {...props}
@@ -63,7 +97,7 @@ export const Markdown = (
     <ReactMarkdown
       components={components}
       remarkPlugins={[remarkGfm]}
-      rehypePlugins={[rehypeRaw, rehypeSanitize]}
+      rehypePlugins={[[rehypeSanitize, sanitizeSchema]]}
       {...props}
     />
   );
@@ -165,6 +199,7 @@ const componentsInheritFonts: ComponentProps<
     <a
       className={clsx(className, classes.common, classes.inheritFonts)}
       target="_blank"
+      rel="noopener noreferrer"
       style={{ ...style, color: palette.primary.main }}
       {...props}
     >
@@ -180,7 +215,7 @@ export const MarkdownInheritFonts = (
     <ReactMarkdown
       components={componentsInheritFonts}
       remarkPlugins={[remarkGfm]}
-      rehypePlugins={[rehypeRaw, rehypeSanitize]}
+      rehypePlugins={[[rehypeSanitize, sanitizeSchema]]}
       {...props}
     />
   );

From 9e949c27e2ef8935837fd1e1ad8afd2279f40e37 Mon Sep 17 00:00:00 2001
From: Max Burri <burri@puzzle.ch>
Date: Wed, 8 Jul 2026 14:05:31 +0000
Subject: [PATCH 2/4] doc: add changelog entry

---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8e62e13b8..8fc60a5a4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,9 +11,9 @@ You can also check the
 
 ## Unreleased
 
-
 - Fixes
   - Correctly set CSP headers for index pages
+  - Harden markdown renderer sanitization
 
 - Maintenance
   - Add dev-container support

From 5396a7fe919de1bbfbae55a1788789ef29a1a3b9 Mon Sep 17 00:00:00 2001
From: Max Burri <burri@puzzle.ch>
Date: Wed, 8 Jul 2026 14:11:32 +0000
Subject: [PATCH 3/4] chore: remove unused dependency

---
 app/package.json | 1 -
 1 file changed, 1 deletion(-)

diff --git a/app/package.json b/app/package.json
index 2aa8f0394..cf046c6d1 100644
--- a/app/package.json
+++ b/app/package.json
@@ -153,7 +153,6 @@
     "react-transition-group": "^4.4.5",
     "react-virtualized-auto-sizer": "^1.0.25",
     "react-window": "^1.8.10",
-    "rehype-raw": "^7.0.0",
     "rehype-sanitize": "^6.0.0",
     "remark-gfm": "^4.0.0",
     "simple-statistics": "^7.6.0",

From a43c275652cce67fef3d39a591efc209c625e83a Mon Sep 17 00:00:00 2001
From: Max Burri <burri@puzzle.ch>
Date: Wed, 8 Jul 2026 14:22:54 +0000
Subject: [PATCH 4/4] chore: fixes after review

---
 app/components/markdown.tsx | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/app/components/markdown.tsx b/app/components/markdown.tsx
index f69e4a954..7dca5c1fe 100644
--- a/app/components/markdown.tsx
+++ b/app/components/markdown.tsx
@@ -34,10 +34,8 @@ const sanitizeSchema = {
   ],
   attributes: {
     ...defaultSchema.attributes,
-    a: ["href", "title", "target"],
-    "*": (defaultSchema.attributes?.["*"] ?? []).filter(
-      (attr) => !(typeof attr === "string" && attr.startsWith("on"))
-    ),
+    a: ["href", "title"],
+    "*": defaultSchema.attributes?.["*"] ?? [],
   },
 };
 
@@ -79,11 +77,11 @@ const components: ComponentProps<typeof ReactMarkdown>["components"] = {
   ),
   a: ({ children, className, style, ...props }) => (
     <a
+      {...props}
       target="_blank"
       rel="noopener noreferrer"
       className={clsx(className, classes.common)}
       style={{ ...style, color: palette.primary.main }}
-      {...props}
     >
       {children}
     </a>
@@ -115,7 +113,11 @@ export const InlineMarkdown = ({
         p: ({ children }) => <>{children}</>,
         strong: ({ children }) => <strong>{children}</strong>,
         em: ({ children }) => <em>{children}</em>,
-        a: ({ children, href }) => <a href={href}>{children}</a>,
+        a: ({ children, href }) => {
+          const safeHref =
+            href && /^(https?|mailto|ircs?):/i.test(href) ? href : undefined;
+          return <a href={safeHref}>{children}</a>;
+        },
         h1: () => null,
         h2: () => null,
         h3: () => null,
@@ -197,11 +199,11 @@ const componentsInheritFonts: ComponentProps<
   ),
   a: ({ children, className, style, ...props }) => (
     <a
+      {...props}
       className={clsx(className, classes.common, classes.inheritFonts)}
       target="_blank"
       rel="noopener noreferrer"
       style={{ ...style, color: palette.primary.main }}
-      {...props}
     >
       {children}
     </a>