StudioCMS S3 Storage Manager Authorization Bypass via Missing `await` on Async Auth Check

published 2026-03-11 7 mo ago modified 2026-06-17 4 mo ago also GHSA-mm78-fgq8-6pgr , EUVD-2026-11367

cvss: 7.6; 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 11%
public exploits: 0; none known

StudioCMS is a server-side-rendered, Astro native, headless content management system. Prior to 0.3.1, the S3 storage manager's isAuthorized() function is declared async (returns Promise<boolean>) but is called without await in both the POST and PUT handlers. Since a Promise object is always truthy in JavaScript, !isAuthorized(type) always evaluates to false, completely bypassing the authorization check. Any authenticated user with the lowest visitor role can upload, delete, rename, and list all files in the S3 bucket. This vulnerability is fixed in 0.3.1.

Patch / fix

fixed in 2

npm @studiocms/s3-storage 0.3.1
studiocms studiocms 0.3.1

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: partial
Assessed: 7 mo ago (2026-03-12)

Exploit prediction

0.21% chance of exploitation in the next 30 days, higher than 11% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/withstudiocms/studiocms/security/advisories/GHSA-mm78-fgq8-6pgr referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	7.6	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:L
NVD	3.1	6.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
GitHub	3.1	7.6	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:L

Affected packages

ecosystem	package	affected	fixed in
npm	@studiocms/s3-storage	<0.3.1	0.3.1

Affected products

@studiocms s3-storage

Classification

Weakness

CWE-863 Incorrect Authorization

References

github.com /withstudiocms/studiocms/security/advisories/GHSA-mm78-fgq8-6pgr
web, exploit, vendor-advisory
nvd.nist.gov /vuln/detail/CVE-2026-32101
advisory
github.com /withstudiocms/studiocms
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