Deserialization of Untrusted Data Affecting october/system package, versions <3.7.17>=4.0.0, <4.2.23
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published28 Sept 2026
- disclosed14 Sept 2026
- creditUnknown
Introduced: 14 Sep 2026
NewCVE-2026-49400 (opens in a new tab)How to fix?
Upgrade october/system to version 3.7.17, 4.2.23 or higher.
Overview
october/system is a System module for October CMS.
Affected versions of this package are vulnerable to Deserialization of Untrusted Data in the SessionMaker process. An attacker can execute arbitrary PHP code by injecting a crafted serialized payload into the widget.* session key, which is then deserialized without class restrictions. This is only exploitable if cms.safe_mode is enabled and a backend user with CMS markup editing access is present who is not intended to be trusted as a full administrator. A suitable PHP gadget chain must also be reachable from the installed dependency set.
Workaround
This vulnerability can be mitigated by restricting CMS markup editing access to fully trusted administrators only.
Details
Serialization is a process of converting an object into a sequence of bytes which can be persisted to a disk or database or can be sent through streams. The reverse process of creating object from sequence of bytes is called deserialization. Serialization is commonly used for communication (sharing objects between multiple hosts) and persistence (store the object state in a file or a database). It is an integral part of popular protocols like Remote Method Invocation (RMI), Java Management Extension (JMX), Java Messaging System (JMS), Action Message Format (AMF), Java Server Faces (JSF) ViewState, etc.
Deserialization of untrusted data (CWE-502) is when the application deserializes untrusted data without sufficiently verifying that the resulting data will be valid, thus allowing the attacker to control the state or the flow of the execution.