fixes a possible 'javascript:' protocol exploit [backport:1.0] (#19134)

* fixes a possible 'javascript:' protocol exploit [backport:1.0]

* add tests

* Update tests/stdlib/trstgen.nim

* add the same logic for hyperlinks

* move the logic into a proc

Co-authored-by: narimiran <narimiran@disroot.org>
(cherry picked from commit 9338aa2497)

lib/packages/docutils/rstgen.nim

@@ -26,7 +26,7 @@
 ## **Note:** Import ``packages/docutils/rstgen`` to use this module
 
 import strutils, os, hashes, strtabs, rstast, rst, highlite, tables, sequtils,
-  algorithm, parseutils
+  algorithm, parseutils, strscans
 
 import ../../std/private/since
 
@@ -786,6 +786,16 @@ proc renderOverline(d: PDoc, n: PRstNode, result: var string) =
         rstnodeToRefname(n), tmp, $chr(n.level - 1 + ord('A'))])
 
 
+proc safeProtocol(linkStr: var string) =
+  var protocol = ""
+  if scanf(linkStr, "$w:", protocol):
+    # if it has a protocol at all, ensure that it's not 'javascript:' or worse:
+    if cmpIgnoreCase(protocol, "http") == 0 or cmpIgnoreCase(protocol, "https") == 0 or
+        cmpIgnoreCase(protocol, "ftp") == 0:
+      discard "it's fine"
+    else:
+      linkStr = ""
+
 proc renderTocEntry(d: PDoc, e: TocEntry, result: var string) =
   dispA(d.target, result,
     "<li><a class=\"reference\" id=\"$1_toc\" href=\"#$1\">$2</a></li>\n",
@@ -850,6 +860,8 @@ proc renderImage(d: PDoc, n: PRstNode, result: var string) =
 
   # support for `:target:` links for images:
   var target = esc(d.target, getFieldValue(n, "target").strip())
+  safeProtocol(target)
+
   if target.len > 0:
     # `htmlOut` needs to be of the following format for link to work for images:
     # <a class="reference external" href="target"><img src=\"$1\"$2/></a>