# CVE-2026-127203: AppFlowy Cloud 0.9.64 Stored XSS via Blob Upload Content-Type

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

AppFlowy Cloud through 0.9.64 contains a stored cross-site scripting vulnerability that allows authenticated workspace members to upload blobs with unvalidated Content-Type values that are later served inline without a Content-Disposition header or authentication on the retrieval route. Attackers can upload a text/html or image/svg+xml blob via put_blob_handler, which is then rendered as an active same-origin document through the unauthenticated get_blob_handler endpoint and cached immutably for one year, enabling persistent script execution against any visitor who accesses the URL.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- AppFlowy-IO / AppFlowy-Cloud (AppFlowy-IO/AppFlowy-Cloud): ≥ 0; ≤ 0.9.64 (affected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 5.1 (medium); CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 5.4 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N; source: CNA: VulnCheck

- CVSS 4.0: 5.1 (medium); CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/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; source: NVD: disclosure@vulncheck.com

- CVSS 3.1: 5.4 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-79

## Exploit evidence

- exploit: https://gist.github.com/mtholmquist/9b9683104fc3b5d78a488c06a6674e5c (CNA: VulnCheck)

## References

- https://gist.github.com/mtholmquist/9b9683104fc3b5d78a488c06a6674e5c (CNA: VulnCheck; technical-description, exploit)

- https://www.vulncheck.com/advisories/appflowy-cloud-stored-xss-via-blob-upload-content-type (CNA: VulnCheck; third-party-advisory)

- https://gist.github.com/mtholmquist/9b9683104fc3b5d78a488c06a6674e5c (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/appflowy-cloud-stored-xss-via-blob-upload-content-type (disclosure@vulncheck.com)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-127203; retrieved 2026-11-12; source updated 2026-11-12

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-127203; retrieved 2026-11-12; source updated 2026-11-12

Revision: ae57b7e5160233f4c9a6a2e2577f5cf80695d09790fe1e49745c1e3ef17e55aa

Canonical: https://y2.dev/cve/CVE-2026-127203

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.