AppFlowy Cloud 0.9.64 Stored XSS via Blob Upload Content-Type

published 2026-11-12 2d ago modified 2026-11-12 2d ago also EUVD-2026-124540

cvss: 5.4; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 8%
public exploits: 0; none known

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.

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Exploit prediction

0.19% chance of exploitation in the next 30 days, higher than 8% of all scored CVEs (FIRST EPSS, 2026-11-14).

Exploits and checks

gist.github.com https://gist.github.com/mtholmquist/9b9683104fc3b5d78a488c06a6674e5c referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	4.0	5.1	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
CNA	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
CNA	4.0	5.1	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
NVD	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Affected products

AppFlowy-IO AppFlowy-Cloud

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

gist.github.com /mtholmquist/9b9683104fc3b5d78a488c06a6674e5c
technical-description, exploit
vulncheck.com /advisories/appflowy-cloud-stored-xss-via-blob-upload-content-type
third-party-advisory

Sources

CVE List CVE-2026-127203
NVD CVE-2026-127203

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.