HeyForm Vulnerable to Stored XSS via Unauthenticated SVG File Upload

published 2026-07-20 3 mo ago modified 2026-07-22 3 mo ago also EUVD-2026-45983

cvss: 6.4; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.6%; EPSS 0.6% chance of exploitation in 30 days, percentile 47%
public exploits: 0; none known

HeyForm is an open-source form builder. Prior to version 3.0.0-rc.7, the `/api/upload` endpoint allows unauthenticated file uploads including SVG files. Uploaded SVGs are stored in the static assets directory and served with `Content-Type: image/svg+xml` by Express's serve-static middleware, allowing an attacker to achieve stored cross-site scripting (XSS) on the heyform domain without any authentication. Version 3.0.0-rc.7 contains a patch for the issue.

Patch / fix

links 1

github.com/heyform/heyform@144240e commit

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: partial
Assessed: 3 mo ago (2026-07-20)

Exploit prediction

0.57% chance of exploitation in the next 30 days, higher than 47% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	6.4	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
CNA	4.0	6.4	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/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

Affected products

heyform heyform

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation
CWE-434 Unrestricted Upload of File with Dangerous Type

References

Sources

CVE List CVE-2026-45797
NVD CVE-2026-45797

Fencer Vulns 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.

Summary