Security readout for executives and security teams
Plain-English summary
CMS Made Simple through 2.2.15 has an authenticated file upload flaw that can let a highly privileged remote user place a webshell and take over the site. The main business risk is compromise of the CMS host, content, and data if admin-level accounts are abused or stolen.
Executive priority
Treat as high priority for any exposed CMS Made Simple installation through 2.2.15, especially where admin accounts are shared, weakly protected, or accessible from the internet.
Technical view
CVE-2021-28998 is a CWE-434 unrestricted file upload issue in CMS Made Simple through 2.2.15. The CVSS 3.1 score is 7.2 with network access, low attack complexity, high privileges required, no user interaction, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is most likely where CMS Made Simple versions through 2.2.15 are internet-accessible and have administrative or highly privileged upload capability available to users or compromised accounts.
Exploitation context
The sources describe a crafted PHAR upload leading to remote code execution via webshell. The bundle does not show CISA KEV listing or confirmed active exploitation, so active exploitation should not be claimed from these sources alone.
Researcher notes
The record has strong impact but requires high privileges. Focus validation on confirmed CMS Made Simple assets, version evidence, role exposure, upload controls, and post-compromise indicators. Patch details are not provided in the supplied bundle, so rely on vendor guidance for exact remediation.
Mitigation direction
- Inventory CMS Made Simple deployments and identify versions through 2.2.15.
- Check CMS Made Simple vendor guidance for fixed versions or supported upgrade paths.
- Restrict privileged CMS access to trusted administrators and managed networks.
- Review and tighten file upload permissions for privileged CMS roles.
- Monitor web roots and upload directories for unexpected executable files.
Validation and detection
- Confirm CMS Made Simple version on each exposed instance.
- Review privileged CMS accounts for necessity, MFA, and recent suspicious use.
- Inspect upload and web-accessible directories for unauthorized webshell-like files.
- Review web and application logs for unusual authenticated upload activity.
- Verify remediation against vendor guidance after upgrade or configuration changes.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-434: File access and web shell behavior lookup
File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupFile access behavior lookup
The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-28998 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.2 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H1.25.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.2HighVector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Source materials
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Unrestricted Upload of File with Dangerous Type
Unrestricted Upload of File with Dangerous Type represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.