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.
Affected products
python: python
References7
- mail.python.org/archives/list/[email protected]/thre… Mailing ListVendor Advisory
- github.com/python/cpython/commit/3c59b8b53fc75c7f9578d16fb8201c… Patch
- github.com/python/cpython/commit/76b3923d688c0efc580658476c5f52… Patch
- github.com/python/cpython/commit/f795e042043dfe26c42e1971d4502c… Patch
- github.com/python/cpython/pull/148848 Issue TrackingPatch
- github.com/python/cpython/issues/90309 ExploitIssue Tracking
- cert-portal.siemens.com/productcert/html/ssa-457936.html
Metrics
- CVSS 3.1
-
6.1
MEDIUM
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - CVSS 4.0
-
2.1
LOW
Score source: CNA
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 11 · as of 13 November 2026
- CWE
- CWE-150CWE-116
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.