CVE-2026-40754: WordPress Roisin theme <= 1.4 - PHP Object Injection vulnerability

Synopsis

PHP Object Injection is a class of vulnerability where user-supplied data is fed into PHP's unserialize() function, allowing an attacker to instantiate arbitrary objects and chain them into destructive actions. The Roisin WordPress theme (version 1.4 and earlier) exposes this flaw over the network with no authentication required, making it reachable by any external attacker. Successful exploitation can result in full disclosure of sensitive data, unauthorized modification of site content or backend records, and complete disruption of availability. No upstream fix has been published yet; HarborGuard is tracking the advisory and will make a patched-image rebuild available the moment one is released.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the WordPress installation over the network; there is no requirement for local or physical access.

• AuthenticationNot required

  No account or credentials of any privilege level are needed; the vulnerable deserialization endpoint is accessible to unauthenticated requests.

• Victim interactionNot required

  The attacker does not need to social-engineer or wait on any user action; the exploit is sent directly to the server.

• Attack complexityDetail

  Attack complexity is rated High, meaning reliable exploitation may depend on specific environmental conditions such as the presence of a usable POP chain (a sequence of existing PHP classes that can be chained together to produce a harmful outcome) within the target WordPress installation.

Blast Radius

• A successful attacker reads confidential data stored on the server, including WordPress database credentials, API keys, and stored user records.
• An attacker modifies persisted database rows, injecting malicious content, altering user roles, or planting backdoor accounts.
• An attacker crashes or renders the WordPress application unavailable by triggering destructive object chains during deserialization.
• Depending on available POP chains, an attacker may write arbitrary files to the server filesystem, enabling persistent code execution.