Addressing Security Risks in Digitally Signed PDF Documents

By Yakov Yeroslav, CEO

One of the most formidable cyber threats today involves malicious actors exploiting trusted network channels to infiltrate organizations’ infrastructure via infected files – channels that must remain open for regular business operations.

To combat this evolving threat landscape, organizations are turning to cutting-edge technology known as Content Disarm & Reconstruction (CDR). This sophisticated technology dissects files into their elemental components and rigorously scrutinizes them using an array of tools in a concerted effort to expose vulnerabilities.

However, even if no vulnerabilities are initially detected, there is still a lingering concern. A portion of the file may harbor a concealed threat, one that eludes detection during the initial assessment—a so-called “Zero Day” threat. Consequently, CDR technology proceeds to initiate the file reconstruction process.

During this transformative procedure, the file undergoes a series of alterations designed to encapsulate and neutralize any threats it may harbor. The outcome is a secure, fully functional copy that is virtually indistinguishable from the original.

When it comes to files with digital signatures, such as PDF documents, undergoing the reconstruction process inevitably compromises the signature. This compromise poses a significant challenge in contexts where document authenticity relies heavily on the integrity of the signature. It’s worth noting that PDF files are constructed using elements based on Base64 encoding, which can, on occasion, be exploited to introduce malicious code into the PDF.

So, how can organizations effectively address this problem?

One approach is to conduct threat assessments relying mainly on the inherent detection capabilities of CDR technology. However, it’s important to recognize that detection tools may not always be adept at identifying threats introduced through Base64 encoding. The risk factor remains elevated, especially with PDF files.

An alternative strategy involves deploying a suite of diverse threat detection tools while verifying the validity and integrity of the signature. In the absence of any preliminary detections, the original file can be securely stored within a dedicated, encrypted partition prior to reconstruction. Internally, a copy that has undergone reconstruction, complemented by a lead page containing valid signature details, can be used for daily operations.

The latter option fortifies the organization’s defenses, as all incoming files have undergone rigorous, full CDR processing. In scenarios necessitating the presentation of the original document, such as in legal proceedings, it can be retrieved from the secure partition where it was preserved.

Sasa Software has pioneered a solution to address this challenge, primarily based on the second option. Signature validation is conducted in collaboration with Comda, for Comsign signatures. This proven solution has been operational in numerous financial institutions and healthcare organizations for over three years without incident.


Sasa Software, established in 2013, is a cybersecurity software developer specializing in solutions to protect networks from email and file-borne attacks, utilizing Content Disarm and Reconstruction (CDR) file sanitization technology. 

Sasa Software’s GateScanner suite of CDR solutions currently protects hundreds of critical networks around the globe – in government, energy, critical infrastructure, financial services, maritime and healthcare sectors.

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