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Apply safe_href scheme allowlist to images in safe_mode #714

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Apply safe_href scheme allowlist to images in safe_mode #714

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91f26bf
Apply safe_href scheme allowlist to images in safe_mode
Jul 9, 2026
8c6a66b
Narrow image scheme filter to javascript:/vbscript: only
Jul 10, 2026
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11 changes: 10 additions & 1 deletion lib/markdown2.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3111,8 +3111,17 @@ def process_image(self, url: str, title_attr: str, link_text: str) -> Tuple[str,
This section will be skipped by the link processor
'''
img_class_str = self.md._html_class_str_from_tag("img")
safe_src = self.md._protect_url(url)
if self.md.safe_mode:
# Defense-in-depth: strip schemes that are never valid for an image
# `src` and only serve as XSS vectors. `data:` images, http(s) and
# relative URLs are preserved (and quote-escaped by `_protect_url`),
# matching markdown2's existing image handling.
normalized = re.sub(r"[\s\x00-\x1f]+", "", url).lower()
if normalized.startswith(("javascript:", "vbscript:")):
safe_src = ""
result = (
f'<img src="{self.md._protect_url(url)}"'
f'<img src="{safe_src}"'
f' alt="{self.md._hash_span(_xml_escape_attr(link_text))}"'
f'{title_attr}{img_class_str}{self.md.empty_element_suffix}'
)
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