FormCms avatar upload feature has a stored cross-site scripting (XSS) vulnerability

published 2025-08-28 14 mo ago modified 2026-09-26 44 d ago also GHSA-4fxf-xgrm-8fcj , EUVD-2025-26075

cvss: 6.1; 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 10%
public exploits: 0; none known

FormCms v0.5.5 contains a stored cross-site scripting (XSS) vulnerability in the avatar upload feature. Authenticated users can upload .html files containing malicious JavaScript, which are accessible via a public URL. When a privileged user accesses the file, the script executes in their browser context.

Patch / fix

fixed in 2

nuget FormCMS 0.5.7
formcms formcms 0.5.7

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 14 mo ago (2025-08-28)

Exploit prediction

0.20% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/FormCms/FormCms/issues/27 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CISA ADP	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CNA	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
nuget	FormCMS	<0.5.7	0.5.7

Classification

Weakness

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

References

github.com /FormCms/FormCms/issues/27
web, exploit, issue-tracking
github.com /KKC73/me/blob/main/CVE-2025-56236/README.md
web, third-party-advisory
nvd.nist.gov /vuln/detail/CVE-2025-56236
advisory
github.com /formcms/formcms
package

Sources

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