CVE-2026-17086 in ShortPixel Image Optimizer Plugin
Summary
by MITRE • 09/18/2026
The ShortPixel Image Optimizer – Optimize Images, Convert WebP & AVIF plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 6.5.5 via deserialization of untrusted input . This makes it possible for authenticated attackers, with author-level access and above, to inject a PHP Object. No known POP chain is present in the vulnerable software, which means this vulnerability has no impact unless another plugin or theme containing a POP chain is installed on the site. If a POP chain is present via an additional plugin or theme installed on the target system, it may allow the attacker to perform actions like delete arbitrary files, retrieve sensitive data, or execute code depending on the POP chain present.
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Analysis
by VulDB Data Team • 09/18/2026
The ShortPixel Image Optimizer for WordPress contains a critical PHP Object Injection vulnerability affecting all versions up to and including 6.5.5. This flaw stems from the improper deserialization of untrusted input within the plugin's core functionality. In standard web application security, deserializing data provided by users without rigorous validation or type checking is considered a severe anti-pattern because it allows attackers to manipulate internal object states. The vulnerability specifically arises when the application accepts serialized PHP objects and passes them directly into an unserialize function or similar mechanism without ensuring that the input originates from a trusted source or conforms to expected structures. This lack of integrity verification creates a pathway for malicious actors to inject crafted payloads that alter how subsequent code executes within the WordPress environment.
The attack vector requires authenticated access with at least author-level privileges, which aligns with common privilege escalation scenarios where lower-privileged users attempt to gain higher control over the system. While this requirement limits immediate exploitation by anonymous attackers on public-facing sites, it remains a significant risk for multi-author blogs or platforms where user registration is open and trust levels are not strictly enforced through additional administrative controls. The presence of author-level access means that any registered user who has been granted content creation rights can potentially exploit this flaw if they manage to submit the malicious serialized payload through an interface exposed by the ShortPixel plugin, such as image upload forms or optimization settings pages.
A defining characteristic of this vulnerability is its dependency on external components for actual exploitation impact. The vulnerable software itself does not contain a known PHP Object Injection chain, often referred to as a POP chain, that would allow direct remote code execution upon deserialization alone. Consequently, the immediate technical impact is limited unless an attacker can leverage additional installed plugins or themes that do contain exploitable magic methods and gadget chains. This dependency means that while the vulnerability exists in the codebase, its practical exploitability varies significantly based on the specific ecosystem of extensions active on a given WordPress installation. Attackers must therefore perform reconnaissance to identify compatible POP chains within other software components before attempting exploitation.
If a suitable POP chain is present elsewhere on the target system, the consequences can be severe and multifaceted. Successful exploitation could enable an attacker to delete arbitrary files from the server filesystem, potentially destroying critical configuration data or core WordPress files. It may also allow for the retrieval of sensitive information stored in object properties, such as database credentials or API keys embedded within other plugins' objects. In more complex scenarios involving specific gadget chains, this vulnerability can serve as a stepping stone to achieve arbitrary code execution, effectively granting full control over the web server and allowing further lateral movement within the network infrastructure.
From an industry standards perspective, this issue maps directly to CWE-502, which describes Deserialization of Untrusted Data. This category highlights risks associated with accepting serialized objects from unverified sources without proper validation or integrity checks. Furthermore, in terms of tactical classification under MITRE ATT&CK for Enterprise, this vulnerability facilitates the Initial Access and Privilege Escalation techniques by allowing an authenticated user to manipulate application state beyond their intended permissions. It also relates to CWE-94, Improper Control of Generation of Code (Code Injection), as the ultimate goal often involves executing arbitrary commands through manipulated object states that trigger unintended code paths within dependent libraries or plugins.
Mitigation strategies should prioritize immediate remediation by updating the ShortPixel Image Optimizer plugin to a version newer than 6.5.5, where this deserialization flaw has been addressed with proper input validation and type checking mechanisms. Administrators must also audit their installed plugins and themes for known vulnerabilities that might provide exploitable POP chains, as removing unnecessary or outdated extensions reduces the attack surface significantly. Implementing strict least-privilege principles by limiting author-level access to trusted individuals only adds another layer of defense against potential exploitation attempts. Additionally, deploying a Web Application Firewall with rules capable of detecting anomalous serialized data patterns can help block malicious payloads before they reach the vulnerable deserialization logic, providing an effective compensating control while updates are being applied across the infrastructure.