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A Stealthy Entry Point for Cyberattackers: Remote Code Execution via Kerberos File Uploads
A dangerous vulnerability has been discovered in Denodo Scheduler, a widely-used Java-based application for data integration and extraction jobs. Security researchers have identified that attackers can exploit this flaw to remotely execute arbitrary code, potentially compromising entire enterprise environments. Tracked under CVE-2025-26147, the issue stems from how the application handles Kerberos keytab file uploads. Specifically, it fails to properly validate the filenames, enabling path traversal attacks.
This bug affects version 8.0.202309140 of Denodo Scheduler, and a fix has already been issued in update denodo-v80-update-20240307. The vulnerability lies in the way multipart form data is processed — attackers can manipulate file paths using directory traversal sequences like ../../ to upload malicious files to unintended locations on the server. Once uploaded, these files can be accessed and executed, allowing the attacker to take over the system.
The issue becomes even more dangerous when paired with the Java-based architecture of Denodo Scheduler, which typically runs on Apache Tomcat. By targeting the Tomcat webroot, attackers can drop a JSP-based web shell, providing remote access through a web interface. This backdoor lets them run arbitrary commands, essentially giving them full control over the compromised server.
Organizations using vulnerable versions are urged to apply the patch immediately and conduct forensic reviews of their systems to ensure they haven’t already been breached.
What Undercode Say:
This flaw in Denodo Scheduler is a textbook example of how small oversights in input validation can lead to devastating consequences. The vulnerability—tied to improper filename handling in keytab file uploads—offers attackers an ideal entry point to gain persistent access to a server.
The Denodo Scheduler’s use in enterprise environments makes this issue even more critical. As a core tool for orchestrating data workflows, its compromise could ripple through an organization’s entire data infrastructure. This isn’t just about data theft; attackers gaining full control through a web shell could alter, delete, or exfiltrate sensitive information, and even pivot to other internal systems.
The presence of Apache Tomcat as the underlying server adds another layer of risk. Apache Tomcat is a popular target due to its widespread use and the fact that it readily executes JSP files. By exploiting the directory traversal vulnerability to drop a JSP web shell into the webroot, attackers bypass multiple layers of security—authentication, file integrity, and process isolation.
What’s more, Denodo’s attempt to append timestamps to uploaded files for uniqueness actually works against them. Since the server sends the full filename (with the timestamp) back in the response, it inadvertently hands the attacker all the information needed to trigger the malicious code later.
This vulnerability also highlights the dangers of overly trusting administrative interfaces. Web-based admin consoles, especially those dealing with authentication mechanisms like Kerberos, need airtight security. The fact that such a critical operation—uploading Kerberos keytabs—was not adequately protected is alarming.
Another key point is that attackers don’t even need deep access or credentials to pull this off. All they need is a way to reach the file upload endpoint. In poorly segmented environments or externally exposed admin panels, this attack becomes trivial to launch.
Organizations must consider isolating such administrative services and limiting access through firewall rules or VPN tunnels. In addition to patching, security teams should also audit server logs, especially looking for suspicious keytab uploads or unexplained file writes to the Tomcat webroot.
This vulnerability, like many before it, underscores the importance of secure development practices, particularly in input sanitization, upload handling, and exposure of debug-level information. As web shells grow more sophisticated and attacker TTPs (Tactics, Techniques, and Procedures) evolve, even seemingly minor flaws can become catastrophic attack vectors.
With CVE-2025-26147, the path from file upload to full control is dangerously short. Enterprises relying on Denodo Scheduler should treat this threat with the urgency it demands.
Fact Checker Results:
✅ Vulnerability is confirmed and patched by Denodo
✅ Path traversal and RCE chain fully verified by researchers
✅ Exploitable via unauthenticated or low-privilege access in some setups 🔥
Prediction:
This Denodo Scheduler vulnerability will likely become part of automated exploit kits targeting Java web apps in 2025. As attackers often scan for known CVEs with reliable RCE payloads, any unpatched enterprise instance could be breached within days of public disclosure. Expect more sophisticated variants of this attack, including payload obfuscation and chained exploits, as this vulnerability becomes widely weaponized in the cybersecurity underground.
References:
Reported By: cyberpress.org
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