CVE-2026-6879

`Element.findall()` and fully-consumed `Element.iterfind()` exhibit `O(n^2)` time complexity when using XPath index predicates (e.g. `[1]`, `[last()]`, `[last()-N]`) on XML documents with many same-tag siblings. `Element.find()` is only affected when the first match is near the end  of the sibling list, such as with `[last()]` or `[last()-N]`;  `.//item[1]` short-circuits after the first match.

We have discovered 458 live websites that are affected by CVE-2026-6879.

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Affected Software

Product	CPython
Category	Programming Languages
Vulnerable Domains	458 live websites (100% of CPython install base)
Vulnerable Versions	from 0 through 3.15
Vulnerable Versions Count	69 versions ( 100% of all versions)