diff --git a/shared/editor/components/Image.tsx b/shared/editor/components/Image.tsx
index 2f41d1f0d6..ceab3a8b17 100644
--- a/shared/editor/components/Image.tsx
+++ b/shared/editor/components/Image.tsx
@@ -6,7 +6,7 @@ import { useTranslation } from "react-i18next";
 import { find } from "es-toolkit/compat";
 import Flex from "../../components/Flex";
 import { s } from "../../styles";
-import { isExternalUrl, sanitizeUrl } from "../../utils/urls";
+import { isExternalUrl, sanitizeImageSrc } from "../../utils/urls";
 import { EditorStyleHelper } from "../styles/EditorStyleHelper";
 import type { ComponentProps } from "../types";
 import { ResizeLeft, ResizeRight } from "./ResizeHandle";
@@ -68,7 +68,7 @@ const Image = (props: Props) => {
     }
   }, [node.attrs.width]);
 
-  const sanitizedSrc = sanitizeUrl(src);
+  const sanitizedSrc = sanitizeImageSrc(src);
   const linkMarkType = props.view.state.schema.marks.link;
   const imgLink =
     find(node.attrs.marks ?? [], (mark) => mark.type === linkMarkType.name)
diff --git a/shared/editor/lib/Lightbox.ts b/shared/editor/lib/Lightbox.ts
index 9d1643501c..91f02e4c90 100644
--- a/shared/editor/lib/Lightbox.ts
+++ b/shared/editor/lib/Lightbox.ts
@@ -1,7 +1,7 @@
 import type { Node } from "prosemirror-model";
 import { isMermaid } from "./isCode";
 import type { EditorView } from "prosemirror-view";
-import { sanitizeUrl } from "@shared/utils/urls";
+import { sanitizeImageSrc } from "@shared/utils/urls";
 
 export abstract class LightboxImage {
   public pos: number;
@@ -21,7 +21,7 @@ class LightboxRegularImage extends LightboxImage {
     super();
     this.pos = pos;
     const node = view.state.doc.nodeAt(pos);
-    this.src = sanitizeUrl(node?.attrs.src) ?? "";
+    this.src = sanitizeImageSrc(node?.attrs.src) ?? "";
     this.alt = node?.attrs.alt ?? "";
     this.source = node?.attrs.source;
     this.element = view.nodeDOM(pos) as HTMLSpanElement;
diff --git a/shared/editor/nodes/Image.tsx b/shared/editor/nodes/Image.tsx
index 1abbbbf291..a01f85ca20 100644
--- a/shared/editor/nodes/Image.tsx
+++ b/shared/editor/nodes/Image.tsx
@@ -9,7 +9,7 @@ import type {
 import type { Command } from "prosemirror-state";
 import { NodeSelection, Plugin, TextSelection } from "prosemirror-state";
 import * as React from "react";
-import { sanitizeUrl } from "../../utils/urls";
+import { sanitizeImageSrc } from "../../utils/urls";
 import Caption from "../components/Caption";
 import ImageComponent from "../components/Image";
 import type { MarkdownSerializerState } from "../lib/markdown/serializer";
@@ -88,7 +88,7 @@ export const downloadImageNode = async (
     if (cache !== "reload") {
       await downloadImageNode(node, "reload");
     } else {
-      window.open(sanitizeUrl(node.attrs.src), "_blank");
+      window.open(sanitizeImageSrc(node.attrs.src), "_blank");
     }
   }
 };
@@ -211,7 +211,7 @@ export default class Image extends SimpleImage {
             "img",
             {
               ...node.attrs,
-              src: sanitizeUrl(node.attrs.src),
+              src: sanitizeImageSrc(node.attrs.src),
               width: node.attrs.width,
               height: node.attrs.height,
               contentEditable: "false",
diff --git a/shared/editor/nodes/SimpleImage.tsx b/shared/editor/nodes/SimpleImage.tsx
index 07d12e2571..5f7439fac6 100644
--- a/shared/editor/nodes/SimpleImage.tsx
+++ b/shared/editor/nodes/SimpleImage.tsx
@@ -10,7 +10,7 @@ import { TextSelection, NodeSelection } from "prosemirror-state";
 import * as React from "react";
 import type { Primitive } from "utility-types";
 import { getEventFiles } from "../../utils/files";
-import { sanitizeUrl } from "../../utils/urls";
+import { sanitizeImageSrc } from "../../utils/urls";
 import { AttachmentValidation } from "../../validations";
 import type { Options } from "../commands/insertFiles";
 import insertFiles from "../commands/insertFiles";
@@ -77,7 +77,7 @@ export default class SimpleImage extends Node {
           "img",
           {
             ...node.attrs,
-            src: sanitizeUrl(node.attrs.src),
+            src: sanitizeImageSrc(node.attrs.src),
             contentEditable: "false",
           },
         ],
diff --git a/shared/utils/urls.test.ts b/shared/utils/urls.test.ts
index 4225433050..80f402c091 100644
--- a/shared/utils/urls.test.ts
+++ b/shared/utils/urls.test.ts
@@ -193,6 +193,16 @@ describe("sanitizeUrl", () => {
   });
 
   describe("Blocked protocols", () => {
+    it("should sanitize base64-encoded image data URIs (links should not embed data)", () => {
+      expect(
+        urlsUtils.sanitizeUrl(
+          "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII="
+        )
+      ).toEqual(
+        "https://data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII="
+      );
+    });
+
     it("should be sanitized", () => {
       expect(urlsUtils.sanitizeUrl("file://localhost.com/outline.txt")).toEqual(
         "https://file://localhost.com/outline.txt"
@@ -210,6 +220,62 @@ describe("sanitizeUrl", () => {
   });
 });
 
+describe("sanitizeImageSrc", () => {
+  it("should return undefined if not a src", () => {
+    expect(urlsUtils.sanitizeImageSrc(undefined)).toBeUndefined();
+    expect(urlsUtils.sanitizeImageSrc(null)).toBeUndefined();
+    expect(urlsUtils.sanitizeImageSrc("")).toBeUndefined();
+  });
+
+  it("should return base64-encoded image data URIs unchanged", () => {
+    const png =
+      "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=";
+    expect(urlsUtils.sanitizeImageSrc(png)).toEqual(png);
+    const gif =
+      "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7";
+    expect(urlsUtils.sanitizeImageSrc(gif)).toEqual(gif);
+    const jpeg = "data:image/jpeg;base64,/9j/4AAQSkZJRg==";
+    expect(urlsUtils.sanitizeImageSrc(jpeg)).toEqual(jpeg);
+    const webp = "data:image/webp;base64,UklGRh4AAABXRUJQVlA4TBEAAAAvAAAAAA";
+    expect(urlsUtils.sanitizeImageSrc(webp)).toEqual(webp);
+    const avif = "data:image/avif;base64,AAAAHGZ0eXBhdmlmAAAAAGF2aWY";
+    expect(urlsUtils.sanitizeImageSrc(avif)).toEqual(avif);
+  });
+
+  it("should sanitize svg data URIs (can contain inline scripts)", () => {
+    expect(
+      urlsUtils.sanitizeImageSrc("data:image/svg+xml;base64,PHN2Zy8+")
+    ).toEqual("https://data:image/svg+xml;base64,PHN2Zy8+");
+    expect(
+      urlsUtils.sanitizeImageSrc("data:image/svg;base64,PHN2Zy8+")
+    ).toEqual("https://data:image/svg;base64,PHN2Zy8+");
+    expect(
+      urlsUtils.sanitizeImageSrc("data:image/SVG+XML;base64,PHN2Zy8+")
+    ).toEqual("https://data:image/SVG+XML;base64,PHN2Zy8+");
+    expect(
+      urlsUtils.sanitizeImageSrc("data:image/svg+xml,<svg></svg>")
+    ).toEqual("https://data:image/svg+xml,<svg></svg>");
+  });
+
+  it("should sanitize non-image data URIs", () => {
+    expect(
+      urlsUtils.sanitizeImageSrc("data:text/html,<script>alert('hi');</script>")
+    ).toEqual("https://data:text/html,<script>alert('hi');</script>");
+  });
+
+  it("should fall through to sanitizeUrl behavior for non-data-URI input", () => {
+    expect(urlsUtils.sanitizeImageSrc("https://example.com/a.png")).toEqual(
+      "https://example.com/a.png"
+    );
+    expect(urlsUtils.sanitizeImageSrc("/uploads/a.png")).toEqual(
+      "/uploads/a.png"
+    );
+    expect(urlsUtils.sanitizeImageSrc("javascript:alert(1)")).toEqual(
+      "https://javascript:alert(1)"
+    );
+  });
+});
+
 describe("parseShareIdFromUrl", () => {
   it("should return share id from url with doc path", () => {
     expect(
diff --git a/shared/utils/urls.ts b/shared/utils/urls.ts
index 7836363a59..03b5987af9 100644
--- a/shared/utils/urls.ts
+++ b/shared/utils/urls.ts
@@ -179,6 +179,24 @@ export function isBase64Url(url: string) {
   return match ? match : false;
 }
 
+const allowedSchemes = [
+  "mailto:",
+  "sms:",
+  "fax:",
+  "tel:",
+  "geo:",
+  "maps:",
+  "magnet:",
+];
+
+const allowedImageDataUris = [
+  "data:image/png;base64,",
+  "data:image/jpeg;base64,",
+  "data:image/gif;base64,",
+  "data:image/webp;base64,",
+  "data:image/avif;base64,",
+];
+
 /**
  * For use in the editor, this function will ensure that a url is
  * potentially valid, and filter out unsupported and malicious protocols.
@@ -191,17 +209,7 @@ export function sanitizeUrl(url: string | null | undefined) {
     return undefined;
   }
 
-  const allowedSchemes = [
-    "mailto:",
-    "sms:",
-    "fax:",
-    "tel:",
-    "geo:",
-    "maps:",
-    "magnet:",
-  ];
   const lower = url.toLowerCase();
-
   if (
     !isUrl(url, { requireHostname: false }) &&
     !url.startsWith("/") &&
@@ -213,6 +221,27 @@ export function sanitizeUrl(url: string | null | undefined) {
   return url;
 }
 
+/**
+ * For use in the editor on image-like elements, this function will ensure
+ * that a src is potentially valid. In addition to the protocols allowed by
+ * `sanitizeUrl`, base64-encoded image data URIs are permitted (excluding
+ * SVG, which can contain inline scripts).
+ *
+ * @param src The src to sanitize.
+ * @returns The sanitized src.
+ */
+export function sanitizeImageSrc(src: string | null | undefined) {
+  if (!src) {
+    return undefined;
+  }
+
+  const lower = src.toLowerCase();
+  if (allowedImageDataUris.some((scheme) => lower.startsWith(scheme))) {
+    return src;
+  }
+  return sanitizeUrl(src);
+}
+
 /**
  * Returns a regex to match the given url.
  *