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CVE Record

CVE-2021-34667: Calendar_plugin <= 1.0 Reflected Cross-Site Scripting

The Calendar_plugin WordPress plugin is vulnerable to Reflected Cross-Site Scripting due to the use of `$_SERVER['PHP_SELF']` in the ~/calendar.php file which allows attackers to inject arbitrary web scripts, in versions up to and including 1.0.

MediumCVSS 6.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

Calendar_plugin for WordPress version 1.0 and earlier can reflect attacker-supplied script into a user's browser. The business risk is account or session impact if a victim follows a malicious link while using an affected site. The source bundle does not show active exploitation or a named fixed version.

Executive priority

Treat as a moderate-priority web application risk. Prioritize internet-facing WordPress sites and sites used by administrators or customers, but do not treat this as known active exploitation based on the supplied evidence.

Technical view

The plugin's ~/calendar.php uses $_SERVER['PHP_SELF'] in a way that enables reflected cross-site scripting. CVSS 3.1 is 6.1 with network access, low complexity, no privileges required, user interaction required, changed scope, and low confidentiality and integrity impact.

Likely exposure

Exposure is likely limited to WordPress sites that have Calendar_plugin installed at version 1.0 or earlier. Risk is higher where authenticated users, administrators, or customers can be induced to follow links to affected pages.

Exploitation context

The bundle identifies reflected XSS, which generally requires user interaction. CISA KEV status is false, and the supplied sources do not state active exploitation, public weaponization, or exploitation at scale.

Researcher notes

Mapped to CWE-79. The affected record names Calendar_plugin 1.0 with no CPEs. Evidence supports the vulnerable cause and version range, but patch availability and exploitation status are not established in the bundle.

Mitigation direction

  • Inventory WordPress sites for Calendar_plugin version 1.0 or earlier.
  • Check vendor or WordPress plugin guidance for an official fixed version.
  • Disable or remove the plugin where it is unnecessary or unsupported.
  • Apply a vendor-supported update if one is available.
  • Use defensive controls such as WAF rules and CSP as compensating measures.

Validation and detection

  • Confirm whether Calendar_plugin is installed and active on WordPress sites.
  • Record the exact plugin version and deployment locations.
  • Review application logs for unusual requests involving calendar.php.
  • Verify whether vendor guidance names a patched release or removal path.
  • Retest after remediation to confirm reflected script input is not rendered.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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 · medium confidence lookup

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 lookup
cve · low confidence lookup

CVE-2021-34667 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
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

Official CVE source material

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.

1CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS vector scores

1 official score

We 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.

ScoreVersionSeverityVectorExploitImpactSource
6.1CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N2.82.7Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.1Medium
CVSS 3.1 vector shape for CVE-2021-34667Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Calendar_pluginCalendar_plugin1.0Listed
Weakness

CWE details

CWE-79

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.