Skip to content

Fix quadratic-time backtracking in attr_list attribute regex #1656

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
naaz234 wants to merge 3 commits into
base: master
Choose a base branch
from
Open

Fix quadratic-time backtracking in attr_list attribute regex #1656

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
09d3a7f
Fix quadratic-time backtracking in attr_list attribute regex
naaz234 Oct 14, 2026
f89d65d
Reference PR number in attr_list changelog entry
naaz234 Oct 19, 2026
dae12eb
Merge branch 'master' into attr-list-quadratic-backtracking
waylan Oct 19, 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
3 changes: 3 additions & 0 deletions docs/changelog.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -16,6 +16,9 @@ See the [Contributing Guide](contributing.md) for details.

### Fixed

* Fix quadratic-time regex backtracking in `attr_list` when a block ends with an
unclosed attribute list followed by a long run of spaces, e.g. a line
consisting only of `{` and some text with many trailing spaces (#1656).
* For backwards compatibility in some languages, revert the enforcement of CommonMark
style punctuation rules (#1657).

Expand Down
2 changes: 1 addition & 1 deletion markdown/extensions/attr_list.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -90,7 +90,7 @@ def isheader(elem: Element) -> bool:

class AttrListTreeprocessor(Treeprocessor):

BASE_RE = r'\{\:?[ ]*([^\}\n ][^\n]*)[ ]*\}'
BASE_RE = r'\{\:?[ ]*([^\}\n ][^\n]*)\}'
HEADER_RE = re.compile(r'[ ]+{}[ ]*$'.format(BASE_RE))
BLOCK_RE = re.compile(r'\n[ ]*{}[ ]*$'.format(BASE_RE))
INLINE_RE = re.compile(r'^{}'.format(BASE_RE))
Expand Down
12 changes: 12 additions & 0 deletions tests/test_syntax/extensions/test_attr_list.py
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -78,6 +78,18 @@ def test_backslash_escape_value(self):
'<h1 id="*Foo*"><code>*Foo*</code></h1>'
)

def test_unclosed_curly_with_long_run_of_spaces(self):
"""
An unclosed attribute list followed by a long run of spaces should be
left as plain text, no matter how many trailing spaces there are.

The content and the trailing spaces both match the same part of the
pattern, so without care the regex backtracks quadratically over the

@waylan waylan Oct 19, 2026

Copy link
Copy Markdown
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

The spellchecker does not recognize "quadratically" as a valid word. Either the comment needs to be rewritten to not use the word, or the word should be added to the dictionary at .spell-dict.

spaces while failing to find the closing brace.
"""
text = 'foo\n{a' + (' ' * 50000)
self.assertMarkdownRenders(text, f'<p>{text}</p>')

def test_table_td(self):
self.assertMarkdownRenders(
self.dedent(
Expand Down
Loading