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.
Weakness
`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.
References
- https://github.com/python/cpython/commit/02c08e6b747ac43d0d866a4ffa916bedf3423f81
- https://github.com/python/cpython/commit/037965c00a427cba5c05447efadc67c51a492e85
- https://github.com/python/cpython/commit/0583f24ae678993e3f7939f51ad5bcae5ad9dc70
- https://github.com/python/cpython/commit/2ffab083782968a4d732738f4f1dff6bbd69d2b0
- https://github.com/python/cpython/commit/390337b8ba1658833fdef379e1739c9f9533a8db
- https://github.com/python/cpython/commit/96510a3758f4a075f43223afdee3b6ee1a7a7f02
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