CVE-2026-1555Known exploitationPublic exploitNetwork attack vector

Unauthenticated arbitrary file upload via unenforced allowlist

Published Apr 15, 2026 · Updated Apr 15, 2026

Unrestricted file upload in ioTheme WebStack 1.2024 and earlier allows remote attackers to place arbitrary files on the server. The unauthenticated img_upload AJAX hook calls io_img_upload(), which copies the supplied extension into a generated name and renames the temporary file without enforcing its image allowlist. No account or user interaction is required; PHP execution follows when the uploads directory serves the attacker-controlled file through a PHP handler.

CVSS severity9.8
Critical
EPSS probability0.98%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unrestricted file upload in ioTheme WebStack 1.2024 and earlier allows remote attackers to place arbitrary files on the server. The unauthenticated img_upload AJAX hook calls io_img_upload(), which copies the supplied extension into a generated name and renames the temporary file without enforcing its image allowlist. No account or user interaction is required; PHP execution follows when the uploads directory serves the attacker-controlled file through a PHP handler.

The record

CVE
CVE-2026-1555
Published
Apr 15, 2026
Updated
Apr 15, 2026
Vendor
ioTheme
Product
WebStack
Classifications
CWE-434, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 14, 2026Exploitation reportedReported WebStack site compromises
  2. Apr 15, 2026CVE publishedPublication date reported by the CVE source.
  3. Apr 15, 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=0 <=1.2024

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ioTheme · WebStackversion=0 <=1.2024

Published CVSS scores

9.8WordfenceCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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 exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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