{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-50571", "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa", "state": "PUBLISHED", "assignerShortName": "GitHub_M", "dateReserved": "2026-06-04T21:34:34.427Z", "datePublished": "2026-10-27T22:40:54.912Z", "dateUpdated": "2026-10-27T22:40:54.912Z"}, "containers": {"cna": {"title": "WebSub: Reflected script execution through intent-verification challenges", "problemTypes": [{"descriptions": [{"cweId": "CWE-79", "lang": "en", "description": "CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')", "type": "CWE"}]}], "metrics": [{"cvssV3_1": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 5.7, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "REQUIRED", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:H/A:N", "version": "3.1"}}], "references": [{"name": "https://github.com/w3c/websub/security/advisories/GHSA-f4hw-w632-m6wh", "tags": ["x_refsource_CONFIRM"], "url": "https://github.com/w3c/websub/security/advisories/GHSA-f4hw-w632-m6wh"}, {"name": "https://github.com/aaronpk/websub.rocks/commit/c9e24b8815c0d9f43350f0408ce2aedf9aa78ede", "tags": ["x_refsource_MISC"], "url": "https://github.com/aaronpk/websub.rocks/commit/c9e24b8815c0d9f43350f0408ce2aedf9aa78ede"}], "affected": [{"vendor": "w3c", "product": "websub", "versions": [{"version": "= REC-websub-20180123", "status": "affected"}]}], "providerMetadata": {"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa", "shortName": "GitHub_M", "dateUpdated": "2026-10-27T22:40:54.912Z"}, "descriptions": [{"lang": "en", "value": "WebSub is a W3C recommendation produced by the Social Web Working Group. In recommendation REC-websub-20180123, the intent-verification protocol requires a subscriber to echo the `hub.challenge` value, also exposed as `hub_challenge` by some frameworks, but does not require safe response media typing or disabled MIME sniffing. An attacker can initiate a subscription to obtain a callback URL and redirect a victim browser to a crafted verification request containing HTML or JavaScript. Subscribers that return the challenge as `text/html` can execute the reflected content in the subscriber origin, using a victim's existing session to read private data or perform actions, exposing `localStorage` or `sessionStorage` and browser permissions granted to that origin. An alternative uses the verification response as an attacker-controlled same-origin script resource to bypass `script-src 'self'`; this can remain possible with `application/octet-stream` when MIME sniffing is allowed. Safe media typing and `X-Content-Type-Options: nosniff` are both needed to address the described scenarios. WebSub Rocks demonstrated reflection, but the advisory does not establish practical impact on that demonstration site."}], "source": {"advisory": "GHSA-f4hw-w632-m6wh", "discovery": "UNKNOWN"}}}}

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