Security readout for executives and security teams
Plain-English summary
A public WordPress site using Simple Matted Thumbnails 1.01 or older could be tricked into reflecting attacker-controlled script into a visitor’s browser. This is not a server takeover finding, but it can support account/session abuse or content manipulation if a user follows a crafted link.
Executive priority
Treat as a moderate web application risk. Prioritize internet-facing WordPress sites and any site with privileged users who may click external links. The main urgency is reducing phishing-assisted browser compromise, not emergency infrastructure containment.
Technical view
CVE-2021-38339 is CWE-79 reflected XSS in simple-matted-thumbnail.php. The plugin reflects $_SERVER["PHP_SELF"] without safe output handling, enabling arbitrary web script injection. CVSS 3.1 is 6.1: network reachable, low complexity, no privileges, user interaction required, changed scope, low confidentiality and integrity impact.
Likely exposure
Exposure is limited to WordPress installations running Simple Matted Thumbnails version 1.01 or earlier, especially if publicly reachable. The source bundle does not identify affected CPEs or a fixed version.
Exploitation context
The CVE is not listed in KEV, and the supplied sources do not state active exploitation. Practical abuse requires a victim to interact with attacker-controlled content or a crafted link that reaches the vulnerable plugin path.
Researcher notes
The key evidence is the reflected PHP_SELF value in the plugin file and Wordfence/CVE metadata. The bundle does not provide a patch commit, fixed version, exploit-in-the-wild evidence, or detailed environmental prerequisites beyond affected plugin version.
Mitigation direction
- Inventory WordPress sites for Simple Matted Thumbnails 1.01 or older.
- Check vendor or WordPress plugin guidance for a fixed release or replacement.
- Disable or remove the plugin where no maintained safe version is available.
- Apply standard WordPress hardening for admin sessions and least privilege.
- Monitor for unexpected requests targeting the plugin PHP file.
Validation and detection
- Confirm plugin name and version from WordPress administration or asset inventory.
- Verify whether simple-matted-thumbnail.php exists on public WordPress deployments.
- Review vendor advisories for any stated fixed version before upgrading.
- Check web logs for suspicious requests to the plugin file.
- Confirm the plugin is disabled, removed, or replaced after remediation.
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-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. 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 lookupCVE-2021-38339 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
- Medium
- CVSS
- 6.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
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:N/UI:R/S:C/C:L/I:L/A:N2.82.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.1MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://www.wordfence.com/vulnerability-advisories/#CVE-2021-38339CVE reference · x_refsource_MISC
- https://plugins.trac.wordpress.org/browser/simple-matted-thumbnails/tags/1.01/simple-matted-thumbnail.php#L122CVE reference · x_refsource_MISC
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.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.