Newsletters Plugin Unsafe Deserialization Remote Code Execution

The Newsletters WordPress plugin before 4.15 does not prevent deserialization of untrusted input that is stored through a public form, allowing unauthenticated attackers to inject a PHP object and, via a property-oriented gadget chain bundled with the Newsletters WordPress plugin before 4.15, write arbitrary files and execute code on the server.

Casky was already ahead

This CVE exploits attack patterns that Casky's 446matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

CVE-2026-12583 is a critical unsafe deserialization vulnerability in the WordPress Newsletters plugin before version 4.15. The flaw allows unauthenticated attackers to inject malicious PHP objects through a public-facing form, exploiting a gadget chain within the plugin itself to achieve arbitrary file write and remote code execution. This impacts all WordPress installations using the affected plugin version, making it particularly dangerous since WordPress plugins are widely deployed and the vulnerability requires no authentication or user interaction beyond form submission.

Casky's 446 matched skills leverage Claude's extended reasoning to detect the attack patterns across MITRE ATT&CK initial access (TA0001), persistence (TA0043), and execution (TA0002) techniques. Practitioners using Casky would identify suspicious PHP object serialization patterns in form submissions, detect gadget chain exploitation indicators in code execution logs, and recognize post-exploitation file write operations—particularly new files with suspicious timestamps in wp-content directories. The platform's skills would flag the progression from unauthenticated form input → deserialization → arbitrary code execution as a distinctive attack signature, enabling defenders to catch exploitation attempts before persistent backdoors are established.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

446 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-12583.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043 TA0002

Investigate the attack patterns behind CVE-2026-12583

Casky has 446 skills that investigate the attack patterns behind CVE-2026-12583. Run one and get CVSS-scored findings in 3 minutes.

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