#35675: Reduce impact of parsing crafted templates with repeat tags
-----------------------------+-------------------------------------------
Reporter: Jake Howard | Type: Bug
Status: new | Component: Template system
Version: | Severity: Normal
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-----------------------------+-------------------------------------------
The template system uses a regex to extract template tags from text. Given
certain inputs, this can take an excessive amount of time:
{{{#!python
In [2]: %timeit Template("{%" * 2000)
34.7 ms ± 153 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)
In [3]: %timeit Template("{%" * 10000)
877 ms ± 1.49 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
In [4]: %timeit Template("{%" * 20000)
3.49 s ± 47 ms per loop (mean ± std. dev. of 7 runs, 1 loop each)
In [5]: %timeit Template("{%")
11.5 µs ± 55.3 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops
each)
}}}
The cause is excessive backtracking in the
[https://github.com/django/django/blob/b99c608ea10cabc97a6b251cdb6e81ef2a83bdcf/django/template/base.py#L89C23-L89C48
pattern used]. Since the template system is so versatile and performance-
critical, fixing the issue appears non-trivial.
Note: This bug was raised with the Security Team prior to opening, however
was not deemed a security vulnerability since parsing untrusted (or semi-
trusted) templates is
[https://docs.djangoproject.com/en/5.0/topics/templates/ explicitly warned
against].
--
Ticket URL: <https://code.djangoproject.com/ticket/35675>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/010701914c4d055f-bc51cf6f-1c35-4dc1-b572-ce49684d4fff-000000%40eu-central-1.amazonses.com.
