CVE-2023-40555Network attack vector

Unauthenticated PHP object injection via AJAX deserialization

Published Dec 20, 2023 · Updated Apr 28, 2026

PHP object injection in UX Themes Flatsome 3.17.5 and earlier allows remote attackers to inject PHP objects through an AJAX request. The flatsome_ajax_load_instagram handler base64-decodes the unauthenticated data parameter and calls maybe_unserialize before validating its hash. The handler is exposed without authentication by default; a suitable POP chain enables file deletion, data retrieval, or code execution.

CVSS severity8.3
High
EPSS probability0.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

PHP object injection in UX Themes Flatsome 3.17.5 and earlier allows remote attackers to inject PHP objects through an AJAX request. The flatsome_ajax_load_instagram handler base64-decodes the unauthenticated data parameter and calls maybe_unserialize before validating its hash. The handler is exposed without authentication by default; a suitable POP chain enables file deletion, data retrieval, or code execution.

The record

CVE
CVE-2023-40555
Published
Dec 20, 2023
Updated
Apr 28, 2026
Vendor
UX Themes
Product
Flatsome
Classifications
CWE-502, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 20, 2023CVE publishedPublication date reported by the CVE source.
  2. Apr 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=n/a <=3.17.5 changes=[{"at":"3.17.6","status":"unaffected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

UX Themes · Flatsomeversion=n/a <=3.17.5 changes=[{"at":"3.17.6","status":"unaffected"}]

Published CVSS scores

8.3GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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