CVE-2021-28977
CWE-79Published: June 23, 2021· Updated: Jun 17, 2026
Official Description
Cross Site Scripting vulnerability in GetSimpleCMS 3.3.16 in admin/upload.php by adding comments or jpg and other file header information to the content of xla, pages, and gzip files,
Technical Analysis
CVE-2021-28977 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.
Exploitation requires high privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
The vulnerability has a "Changed" scope, meaning successful exploitation can impact components beyond the vulnerable component itself — such as the host operating system or adjacent services.
From a weakness classification perspective (CWE-79): Cross-site scripting (XSS) vulnerabilities allow attackers to inject malicious scripts into web pages viewed by other users.
CVSS v3.1 Vector Breakdown
Affected Vendors & Products
Exploit & PoC Resources
Official Patches & Advisories
All References (2)
Quick Facts
Related CVEs (CWE-79)
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2021-28977 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts