CVE-2026-6019

import http.cookies # Simulate a vulnerable scenario # An attacker controls the value of a cookie, injecting the closing script tag malicious_value = "safe_value</script><script>alert('XSS discovered');//" C = http.cookies.SimpleCookie() C["user_id"] = malicious_value # The application uses js_output() to render the cookie setting script vulnerable_output = C["user_id"].js_output() print("Generated JavaScript output:") print(vulnerable_output) # Explanation: # The output will be: <script>document.cookie = "user_id=safe_value</script><script>alert('XSS discovered');//"; # The browser sees the first </script> and closes the script block, # then executes the injected alert() as a new script tag.

{"cve": {"id": "CVE-2026-6019", "sourceIdentifier": "[email protected]", "published": "2026-04-22T20:16:42.617", "lastModified": "2026-05-18T17:08:04.330", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "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": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "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", "baseScore": 2.1, "baseSeverity": "LOW", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "privilegesRequired": "HIGH", "userInteraction": "NONE", "vulnConfidentialityImpact": "LOW", "vulnIntegrityImpact": "LOW", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N", "baseScore": 6.1, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "CHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.8, "impactScore": 2.7}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-150"}]}, {"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-116"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:python:cpython:*:*:*:*:*:*:*:*", "versionEndExcluding": "3.15.0", "matchCriteriaId": "79DFCBF4-1DAF-4A23-8C12-8AC2642973BA"}]}]}], "references": [{"url": "https://github.com/python/cpython/commit/3c59b8b53fc75c7f9578d16fb8201ceb43e8f76c", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/python/cpython/commit/76b3923d688c0efc580658476c5f525ec8735104", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/python/cpython/commit/f795e042043dfe26c42e1971d4502c1cdc4c65b8", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/python/cpython/issues/90309", "source": "[email protected]", "tags": ["Exploit", "Issue Tracking"]}, {"url": "https://github.com/python/cpython/pull/148848", "source": "[email protected]", "tags": ["Issue Tracking", "Patch"]}, {"url": "https://mail.python.org/archives/list/[email protected]/thread/IVNWGV2BBNC3RHQAFS22UP4DY56SAXX3/", "source": "[email protected]", "tags": ["Vendor Advisory", "Mailing List"]}]}}