Skip to content

Further XSS fixes in link attrs (#703) #705

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
Crozzers wants to merge 3 commits into
base: master
Choose a base branch
from
+24 −2
Open

Further XSS fixes in link attrs (#703) #705

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
3b96ec1
Fix XSS fromn HTML encoded colons in hrefs
Crozzers May 14, 2026
a11ce82
Fix XSS from making javascript: hrefs look like domains with ports
Crozzers May 14, 2026
82b4482
Fix onerror XSS in image title attr
Crozzers May 14, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
6 changes: 5 additions & 1 deletion lib/markdown2.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1537,8 +1537,10 @@ def _safe_href(self):
safe = r'-\w'
# omitted ['"<>] for XSS reasons
less_safe = r'#/\.!#$%&\(\)\+,/:;=\?@\[\]^`\{\}\|~'
# html encoded colon in a URL still functions as a normal colon, so need to detect those
protocol_seperators = [':', '&#x3a;', '&#58;', '&colon;']
# dot seperated hostname, optional port number, not followed by protocol seperator
domain = r'(?:[{}]+(?:\.[{}]+)*)(?:(?<!tel):\d+/?)?(?![^:/]*:/*)'.format(safe, safe)
domain = r'(?:[{}]+(?:\.[{}]+)*)(?:(?<!tel)(?<!javascript):\d+/?)?(?![^:/]*(?:{})/*)'.format(safe, safe, '|'.join(protocol_seperators))
fragment = r'[%s]*' % (safe + less_safe)

return re.compile(r'^(?:({})?({})({})|(#|\.{{,2}}/)({}))$'.format(self._safe_protocols, domain, fragment, fragment), re.I)
Expand Down Expand Up @@ -3269,6 +3271,8 @@ def run(self, text: str):
.replace('*', self.md._escape_table['*'])
.replace('_', self.md._escape_table['_'])
)
if self.md.safe_mode:
title = self.md._hash_span(title)
title_str = f' title="{title}"'
else:
title_str = ''
Expand Down
11 changes: 11 additions & 0 deletions test/tm-cases/xss_smuggling_spans_in_image_attrs.html
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -3,3 +3,14 @@
<p><img src="" alt="&lt;code&gt;&quot; onerror=&quot;alert(1)//&lt;/code&gt;" /></p>

<p><img src="B" alt="A" title="&lt;C D=&quot;E&quot; onerror=alert(origin) &gt;" /></p>

<p><a href="#">x</a></p>

<p><a href="#">x</a></p>

<ul>
<li>
<ul>
<li><img src="x" alt="" title="&lt;code&gt;![](&lt;/code&gt;" /> onerror=alert(origin) )</li>
</ul></li>
</ul>
9 changes: 8 additions & 1 deletion test/tm-cases/xss_smuggling_spans_in_image_attrs.text
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,4 +2,11 @@

![`" onerror="alert(1)//`]()

![A](B "<C D="E" onerror=alert(origin) >")
![A](B "<C D="E" onerror=alert(origin) >")

[x](javascript&#58;alert(origin))

[x](javascript:1/alert(origin))

-
- ![](x '`![](`') onerror=alert(origin) )
Loading