Vulnerability Database

393,544

Total vulnerabilities in the database

October CMS: Incomplete Scheme Validation in Image Resizer — october / october

Improper Input Validation

The image resizer classified external sources by testing whether the source string began with the substring http, and the string-source branch in ResizeImageItem::fromObject() accepted any value containing :// as a URL. As a result, non-http(s) PHP stream wrappers such as phar://, file:// and ftp:// could be stored in the resizer cache and later passed to the underlying image library. On a phar:// path this can lead to metadata deserialization during subsequent file operations.

Exploitation requires an existing template-authoring or backend-configuration primitive that passes untrusted input into the |resize Twig filter (or the ResizeImages::resize() API). The /resize/{file} route itself is a lookup against a cache entry that was previously written by trusted server-side code, and an unauthenticated visitor cannot cause an arbitrary source path to be written into that cache. In October's trust model the Publisher and Developer backend roles that can author templates are already trusted with template code execution, so this is a defense-in-depth hardening rather than an unauthenticated network-to-RCE path.

Impact

  • On installations where a template author has piped untrusted input into |resize without validation, a phar:// source could reach the resizer and trigger metadata deserialization
  • No exposure on default templates or on installations where |resize is only applied to trusted values (uploaded file models, theme assets, static URLs)
  • Hardening; not exploitable from the network without a pre-existing injection primitive on the calling code

Patches

The vulnerability has been patched in v4.3.5.

Workarounds

If upgrading immediately is not possible:

  • Audit template code and backend widget configuration for uses of the |resize filter (or direct ResizeImages::resize() calls) that accept untrusted string input, and validate the scheme is http/https before passing it in

References

  • Reported by 0xGenesi
  • Published: Sep 14, 2026
  • Updated: Sep 15, 2026
  • GHSA: GHSA-2xmm-m4wv-3fjh
  • Severity: Low
  • Exploit:
  • CISA KEV:

CVSS v3:

  • Severity: Low
  • Score: 3.9
  • AV:N/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:L

CWEs:

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

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