CVE-2026-77186: My Calendar <= 3.8.3 - Authenticated (Contributor+) Stored Cross-Site Scripting via ‘fallback’ Shortcode Attribute
Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.
Generated by VEDAS. Scores as of 2026-11-04 15:41 UTC. Rebuilt every few hours from cve-scores, CISA KEV and vedas-signatures. How this works and its limits.
What it is
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.
Description quoted from the CVE record (assigned by Wordfence, published 2026-09-09).
Weakness: CWE-79 Improper Neutralization of Input During Web Page Generation (‘Cross-site Scripting’)
How it can be exploited
Exploitable over the network with low attack complexity needing low privileges and no user interaction. Impact: confidentiality low, integrity low, availability none. CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
CISA assessment (SSVC): CISA has no evidence of exploitation. Automatable: no. Technical impact: partial.
Public exploit evidence (Exploit Observer)
Exploit Observer found 3 code repositories naming this CVE.
Code repositories that name a CVE are often scanners, copies or fakes, and some are malware. Read the code before running anything.
See all 7 references on Exploit Observer
Live scores
- EPSS
- 0.004
low predicted chance of attack - VEDAS
- 0.986
strong exploit evidence - On CISA KEV
- Not listed
- Detection rule
- Suricata
Who is affected
| Product | Affected | Not affected |
|---|---|---|
| joedolson My Calendar, Accessible Event Manager | up to and including 3.8.3 | Not stated |
Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.
How to fix it
No fixed version or vendor advisory is listed in the CVE record yet. Watch the vendor’s security page.
How to detect it
Suricata rules (network detection)
1 rule that alert on traffic matching this exploit: VEDAS CVE-2026-77186 WordPress My Calendar Plugin - Stored XSS via fallback shortcode attribute. Add them to your Suricata rule set and reload.
Show the rules
# CVE-2026-77186 - My Calendar - Accessible Event Manager <= 3.8.3 for WordPress, authenticated
# (Contributor+) stored XSS via the 'fallback' shortcode attribute. The bypass uses hex-encoded
# payloads (e.g. \x3cscript\x3e) that wp_kses_post cannot strip on save because they are literal
# backslash sequences; shortcode_parse_atts() later calls stripcslashes() at render, decoding them
# into real tags before an unescaped sink. Matches the save request whose [my_calendar] fallback
# attribute carries an escaped or raw tag opener.
alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2026-77186 WordPress My Calendar Plugin - Stored XSS via fallback shortcode attribute"; flow:established,to_server; http.request_body; content:"my_calendar"; nocase; fast_pattern; content:"fallback"; nocase; pcre:"/fallback\s*=\s*[\x22\x27]?[^\]]*(?:\x5cx3c|<|%3c|onerror|onload|onmouseover)/i"; classtype:web-application-attack; reference:cve,CVE-2026-77186; reference:url,https://www.exploit.observer/?keyword=CVE-2026-77186&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=wordpress&match=exact; sid:1100606; rev:1;)
CVE-2026-77186.rules on GitHub
References
Other references
- https://www.wordfence.com/threat-intel/vulnerabilities/id/62c8fb1f-6cba-43cc-8aca-70812c29a63d?source=cve
- 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-shortcodes.php#L114
- https://plugins.trac.wordpress.org/browser/my-calendar/trunk/my-calendar.php#L556
- https://github.com/joedolson/my-calendar/commit/89bbf7314fac84cdb89e520e8b7b6d69eee8dd3c
Other databases
Where this comes from
This advisory is generated automatically by VEDAS from: CVE.org record, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.
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