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Medium

My Calendar <= 3.8.3 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'fallback' Shortcode Attribute

Type: advisorySources: OSV

The My Calendar – Accessible Event Manager plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'fallback' Shortcode Attribute in all versions up to, and including, 3.8.3 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The bypass relies on hex-encoded shortcode attribute payloads (e.g. \x3cscript\x3e), which wp_kses_post cannot strip on save because they appear as literal backslash sequences rather than real HTML tags; WordPress core's shortcode_parse_atts() then calls stripcslashes() at render time, decoding the escapes into real angle brackets before they reach the unescaped sink.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-77186
Confirmed fixed CVEs
Not specified
Updated in this feed
6 Nov 2026, 01:15 UTC · Revision 1

Source evidence

My Calendar <= 3.8.3 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'fallback' Shortcode Attribute

core-osv · Original source

Published 9 Sept 2026, 03:28 UTC

The My Calendar – Accessible Event Manager plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'fallback' Shortcode Attribute in all versions up to, and including, 3.8.3 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The bypass relies on hex-encoded shortcode attribute payloads (e.g. \x3cscript\x3e), which wp_kses_post cannot strip on save because they appear as literal backslash sequences rather than real HTML tags; WordPress core's shortcode_parse_atts() then calls stripcslashes() at render time, decoding the escapes into real angle brackets before they reach the unescaped sink.

osv:CVE-2026-77186
Complete source record
{
  "id": "24eb5a1edb0b2477eae16205aedce8d6d412130ccaab0f39856d1602fa0e7911",
  "url": "https://osv.dev/vulnerability/CVE-2026-77186",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "My Calendar <= 3.8.3 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'fallback' Shortcode Attribute",
    "summary": "The My Calendar – Accessible Event Manager plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'fallback' Shortcode Attribute in all versions up to, and including, 3.8.3 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The bypass relies on hex-encoded shortcode attribute payloads (e.g. \\x3cscript\\x3e), which wp_kses_post cannot strip on save because they appear as literal backslash sequences rather than real HTML tags; WordPress core's shortcode_parse_atts() then calls stripcslashes() at render time, decoding the escapes into real angle brackets before they reach the unescaped sink.",
    "evidence": "osv:CVE-2026-77186",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-77186",
      "aliases": [
        "CVE-2026-77186"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/joedolson/my-calendar",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "89bbf7314fac84cdb89e520e8b7b6d69eee8dd3c"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "3.8.3"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "fixed": "89bbf7314fac84cdb89e520e8b7b6d69eee8dd3c"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v3.8.3",
            "v3.8.2",
            "v3.8.1",
            "v3.8.0",
            "v3.7.17",
            "v3.7.16",
            "v3.7.15",
            "v3.7.14",
            "v3.7.13",
            "v3.7.12",
            "v.3.7.11",
            "v3.7.10",
            "v3.7.9",
            "v3.7.8",
            "v3.7.7",
            "v3.7.6",
            "v3.7.5",
            "v3.7.4",
            "v3.7.3",
            "v3.7.2",
            "v3.7.1",
            "v3.7.0",
            "v3.7.0-rc1",
            "v3.7.0-beta",
            "v3.6.16",
            "v3.6.15",
            "v3.6.14",
            "v3.6.13",
            "v3.6.12",
            "v3.6.11",
            "v3.6.10",
            "v3.6.9",
            "v3.6.8",
            "v3.6.7",
            "v3.6.6",
            "v3.6.5",
            "v3.6.4",
            "v3.6.3",
            "v3.6.2",
            "v3.6.1",
            "v3.6.0",
            "v3.6.0-RC1",
            "v3.6.0-beta1",
            "v3.5.21",
            "v3.5.20",
            "v3.5.19",
            "v3.5.18",
            "v3.5.17",
            "v3.5.16",
            "v3.5.15",
            "v3.5.14",
            "v3.5.13",
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            "v3.5.11",
            "v3.5.10",
            "v3.5.9",
            "v3.5.8",
            "v3.5.7",
            "v3.5.6",
            "v3.5.5",
            "v3.5.4",
            "v3.5.3",
            "v3.5.2",
            "v3.5.1",
            "v3.5.0",
            "v3.5.0-rc2",
            "v3.5.0-rc1",
            "v3.5.0-beta3",
            "v3.5.0-beta2",
            "v3.5.0-beta1",
            "v3.5.0-alpha",
            "v3.4.21",
            "v3.4.20",
            "v3.4.19",
            "v3.4.18",
            "v3.4.17",
            "v3.4.16",
            "v3.4.15",
            "v3.4.14",
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            "v3.4.12",
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            "v3.4.10",
            "v3.4.9",
            "v3.4.8",
            "v3.4.7",
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            "v3.4.5",
            "v3.4.4",
            "v3.4.3",
            "v3.4.2",
            "v3.4.1",
            "v3.4.0",
            "v3.4.0-RC-4",
            "v3.4.0-RC-3",
            "v3.4.0-RC-2",
            "v3.4.0-RC-1",
            "v3.4.0-beta-3",
            "v3.4.0-beta-2",
            "v3.4.0-beta-1",
            "v3.3.24.1",
            "v3.3.24",
            "v3.3.23",
            "v3.3.22",
            "v3.3.21",
            "v3.3.20",
            "v3.3.19",
            "v3.3.18",
            "v3.3.17",
            "v3.3.16",
            "v3.3.15",
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            "v3.3.13",
            "v3.3.12",
            "v3.3.11",
            "v3.3.10",
            "v3.3.9",
            "v3.3.8",
            "v3.3.7",
            "v3.3.6",
            "v3.3.5",
            "v3.3.4",
            "v3.3.3",
            "v3.3.2",
            "v3.3.1",
            "v3.3.0",
            "v3.3.0-RC4",
            "v3.3.0-RC3",
            "v3.3.0-RC2",
            "v3.3.0-RC1",
            "v3.3.0-beta-1",
            "v3.3.0-alpha-2",
            "v3.2.17",
            "v3.2.16",
            "v3.2.15",
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            "v3.2.13",
            "v3.2.12",
            "v3.2.11",
            "v3.2.10",
            "v3.2.9",
            "v3.2.8",
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            "v3.2.4",
            "v3.2.3",
            "v3.2.2",
            "v3.2.0",
            "3.2.0-RC1",
            "v3.2.0-beta",
            "v3.1.18",
            "v3.1.17",
            "v3.1.16",
            "v3.1.15",
            "v3.1.14",
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            "v.3.0.6",
            "v3.0.5",
            "v3.0.4",
            "v3.0.3",
            "v3.0.1",
            "v3.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-77186.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:45.880433322Z",
      "provider": "osv",
      "references": [
        "https://plugins.trac.wordpress.org/browser/my-calendar/trunk/my-calendar-shortcodes.php#L114",
        "https://plugins.trac.wordpress.org/browser/my-calendar/trunk/my-calendar-widgets.php#L272",
        "https://plugins.trac.wordpress.org/browser/my-calendar/trunk/my-calendar.php#L556",
        "https://www.wordfence.com/threat-intel/vulnerabilities/id/62c8fb1f-6cba-43cc-8aca-70812c29a63d?source=cve",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/77xxx/CVE-2026-77186.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-77186",
        "https://github.com/joedolson/my-calendar/commit/89bbf7314fac84cdb89e520e8b7b6d69eee8dd3c"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-79"
        ],
        "cna_assigner": "Wordfence",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/77xxx/CVE-2026-77186.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-77186",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 513769,
  "published_at": "2026-09-09T03:28:47.091+00:00"
}