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CVE-2026-65883CriticalCVSS 10.0CVE published 29 July 2026Added to mySites.guru 28 July 2026

Aimy Captcha-Less Form Guard (aimycaptchalessformguard) 18.0 to 20.0 - Unauthenticated PHP Object Injection leading to Remote Code Execution

Aimy Captcha-Less Form Guard versions 18.0 through 20.0 contain an unauthenticated PHP object injection flaw that leads to remote code execution. A forged "clfgd" field submitted to the plugin is deserialised without validation, so an attacker who supplies a crafted value can instantiate arbitrary PHP objects and, with a suitable gadget chain, execute code on the server. This is a captcha plugin that runs on public-facing forms, so the vulnerable code path is reachable by anonymous visitors: no account, no session and no user interaction are required. NVD scores it CVSS 4.0 base 10.0 Critical (AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H). Tracked as CVE-2026-65883, published 29 July 2026; the vendor had shipped 20.1 on 28 July 2026 as a security release before the technical detail was public. Both the free and the PRO edition install under the same element and share one version numbering scheme, so both editions are affected. There is no mitigation short of updating, because the fix ships only in 20.1. Update to 20.1 or later from the Joomla backend, or download it from the vendor. Versions 17.0 and below are outside the range the vendor states as affected. Given this is an unauthenticated RCE on a public form handler, treat any site that ran 18.0 to 20.0 while exposed as potentially compromised and review it for unexpected PHP files and unrecognised administrator accounts.

Is my site affected?

Affected
Aimy Captcha-Less Form Guard from 18.0 up to but not including 20.1
Fixed in
20.1
What to do
Update Aimy Captcha-Less Form Guard to 20.1 or later.
Check whether your sites are affected

How CVE-2026-65883 is scored

The base metrics as Joomla CNA published them, and what each one means for a site running an affected version. Threat and environmental metrics are left out: they describe a moment or a particular install rather than the flaw.

10.0 Critical

CVSS 4.0, scored by Joomla CNA
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

How it is reached

AV:N Attack vector
Network. Reachable across the internet
AC:L Attack complexity
Low. Nothing to work around, it just works
AT:N Attack requirements
None. Works against any affected install
PR:N Privileges required
None. No account needed
UI:N User interaction
None. Nobody has to be tricked into anything

What it does to the site

VC:H Confidentiality
High. Everything the site holds can be read
VI:H Integrity
High. Data and files can be altered at will
VA:H Availability
High. The site can be taken down

What it does beyond the site

SC:H Confidentiality
High. Data on other systems can be read
SI:H Integrity
High. Other systems can be altered
SA:H Availability
High. Other systems can be taken down

Timeline

  1. 28 July 2026mySites.guru check added for Aimy Captcha-Less Form Guard (from 18.0 up to but not including 20.1)
  2. 29 July 2026CVE-2026-65883 record published by its CNA

Rule details

Other vulnerabilities in Aimy Captcha-Less Form Guard

Updating for CVE-2026-65883 alone can leave a site on a release another rule still matches. These are the other flaws we check for in the same extension.

Aimy Captcha-Less Form Guard

Latest safe version: 20.1

References

CVE-2026-65883 questions

Which versions are affected by CVE-2026-65883?
CVE-2026-65883 affects Aimy Captcha-Less Form Guard from 18.0 up to but not including 20.1. The fix is in 20.1.
How do I fix CVE-2026-65883?
Update Aimy Captcha-Less Form Guard to 20.1 or later. Then confirm the installed version on the Joomla administrator's Extensions: Manage screen.
How severe is CVE-2026-65883?
Joomla CNA scores it 10.0 (Critical) under CVSS 4.0. In plain terms: reachable across the internet, no account needed and nobody has to be tricked into anything.

Running an affected version on a site you manage?

A free audit tells you which of your Joomla and WordPress sites run an affected version, which are out of date, and which have not been backed up. No card required. If a site is already compromised, fix.mysites.guru is a single fixed fee per incident, usually resolved the same day.

This check is part of the mySites.guru Joomla vulnerability scanner, which reads every installed extension's version on each audit. Browse the rest of the Joomla vulnerability database.

Rules current as of 5 October 2026.