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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.

PUBLISHED Reserved 2026-04-09 | Published 2026-04-22 | Updated 2026-04-29 | Assigner PSF




LOW: 2.1CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

Problem types

CWE-150 Improper neutralization of escape, meta, or control sequences

Product status

Default status
unaffected

Any version before 3.15.0
affected

Credits

oolongeya (https://github.com/komi22) reporter

Seth Larson (https://github.com/sethmlarson) coordinator

References

github.com/python/cpython/pull/148848 patch

github.com/python/cpython/issues/90309 issue-tracking

mail.python.org/.../thread/IVNWGV2BBNC3RHQAFS22UP4DY56SAXX3/ vendor-advisory

github.com/...ommit/76b3923d688c0efc580658476c5f525ec8735104 patch

github.com/...ommit/3c59b8b53fc75c7f9578d16fb8201ceb43e8f76c patch

github.com/...ommit/f795e042043dfe26c42e1971d4502c1cdc4c65b8 patch

cve.org (CVE-2026-6019)

nvd.nist.gov (CVE-2026-6019)

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