Server-Side Template Injection in PDF Signer via CSRF Token

PDF Signer 3.0 contains a server-side template injection vulnerability that allows unauthenticated attackers to execute arbitrary code by injecting PHP commands through the CSRF-TOKEN cookie parameter. Attackers can craft malicious cookie values containing template injection payloads like shell_exec() to execute system commands and retrieve sensitive information from the server.

Casky was already ahead

This CVE exploits attack patterns that Casky's 301matched 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-2019-25729 exploits a critical server-side template injection (SSTI) vulnerability in PDF Signer 3.0, where attackers inject malicious PHP code through the CSRF-TOKEN cookie parameter to achieve unauthenticated remote code execution. With a CVSS score of 9.8, this vulnerability is particularly dangerous because it requires no authentication and allows attackers to execute arbitrary system commands, retrieve sensitive data, and potentially compromise the entire server. Any organization using PDF Signer 3.0 for document processing is at risk, especially those handling confidential documents where integrity and confidentiality are critical.

Casky.ai's 301 mapped skills leverage Claude's extended reasoning to detect the adversarial techniques underlying this attack. Practitioners using Casky will identify two key MITRE ATT&CK patterns: TA0001 (Initial Access) through the unauthenticated exploitation vector and TA0043 (Reconnaissance) as attackers probe for template injection weaknesses. The platform's skills enable detection of suspicious CSRF-TOKEN cookie values containing template syntax (${...}, {{...}}, or PHP functions like shell_exec()), abnormal process execution chains spawned from web server processes, and unexpected outbound connections following injection attempts. Security teams would observe findings highlighting malicious cookie payloads, server-side code execution indicators, and data exfiltration patterns—allowing them to correlate these signals and respond before attackers establish persistence or move laterally through the infrastructure.

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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 →

301 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2019-25729.

analyzing-apt-group-with-mitre-navigator

threat intelligence · low

Run

analyzing-campaign-attribution-evidence

threat intelligence · low

Run

analyzing-certificate-transparency-for-phishing

threat intelligence · low

Run

MITRE ATT&CK Techniques

TA0001 TA0043

Investigate the attack patterns behind CVE-2019-25729

Casky has 301 skills that investigate the attack patterns behind CVE-2019-25729. Run one and get CVSS-scored findings in 3 minutes.

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