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.
Metrics
CVSS 3.1 6.1/10
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:NWeakness enumeration
Affected software
| Vendor | Product | Versions |
|---|---|---|
| Python Software Foundation | CPython | < 3.13.14; >= 3.14.0a1, < 3.14.5rc1; >= 3.15.0a1, < 3.15.0b1 |
References
- https://github.com/python/cpython/commit/3c59b8b53fc75c7f9578d16fb8201ceb43e8f76cPatch
- https://github.com/python/cpython/commit/76b3923d688c0efc580658476c5f525ec8735104Patch
- https://github.com/python/cpython/commit/f795e042043dfe26c42e1971d4502c1cdc4c65b8Patch
- https://github.com/python/cpython/issues/90309Exploit, Issue Tracking
- https://github.com/python/cpython/pull/148848Issue Tracking, Patch
- https://mail.python.org/archives/list/security-announce@python.org/thread/IVNWGV2BBNC3RHQAFS22UP4DY56SAXX3/Mailing List, Vendor Advisory
Timeline
- Published
- Apr 22, 2026
- Last modified
- Nov 10, 2026
- NVD status
- Modified