VirusTotal Exposes 44 Undetected SVG Files Leveraging Base64 Encoding to Deploy Phishing Pages on Web Browsers

Executive Summary

Publication Date: September 05, 2025

In a recent groundbreaking investigation, VirusTotal has identified 44 undetected SVG files that have been weaponized to deploy Base64-encoded phishing pages. This sophisticated attack vector leverages the inherent flexibility of SVG files, enabling threat actors to bypass conventional security detection methods. The use of Base64 encoding to hide malicious code within a trusted image format poses significant challenges to organizations, as the encoded payload can be dynamically decoded and executed, leading to the generation of convincing phishing pages. The persistence of such tactics signals an evolution in modern cyber threats and requires organizations to reexamine their detection and mitigation strategies, particularly within endpoint security and web application infrastructures.

The observed phenomenon involves an intricate exploitation of the SVG format, wherein attackers embed malicious Base64 strings within files that are commonly permitted in web content, thereby circumventing traditional antivirus and IDS/EDR controls. The dynamic behavior triggered upon browser rendering makes static signature detection largely ineffective, while the inherent obfuscation presents considerable analysis challenges. This report provides a detailed technical overview of the exploited mechanism, the delivery process, and the potential links to advanced persistent threat groups, such as APT29 and APT28. It also outlines comprehensive recommendations for enhancing detection capabilities, improving gateway defenses, and bolstering user awareness.

In this advisory report, the Rescana Cybersecurity Intelligence Team has meticulously synthesized information from credible sources and industry research to ensure that our customers receive actionable insights suited to the advanced threat landscape. With evolving phishing techniques targeting both enterprises and government agencies, it is imperative that security teams embrace dynamic behavioral analysis alongside traditional detection measures. The report additionally assures our clients that Rescana remains at the forefront of cybersecurity innovation, continuously adapting and enhancing our Third Party Risk Management (TPRM) platform to face rapidly evolving challenges.

Technical Information

The technical investigation into the malicious SVG files reveals that attackers are ingeniously embedding Base64-encoded payloads within SVG files. As these files are rendered in web browsers or processed by various applications, the embedded Base64 strings are decoded, which subsequently generates dynamic phishing pages that mimic legitimate online services such as corporate login panels and financial institution portals. This obfuscation, achieved through Base64 encoding—a mechanism that transforms the ASCII data into encoded text—allows the malware to remain hidden from static scanners, while the file itself appears to be a normal vector graphic. The malicious activity is triggered when the payload is executed, resulting in the seamless construction of a phishing page that is difficult to distinguish from authentic interfaces.

The attackers rely on the trusted SVG file format to obfuscate their activities and blend the malicious payload with legitimate web content. This methodology stems from the understanding that SVG files are widely accepted in HTML content and are typically not subject to the same level of scrutiny as executable files or typical script attachments. By embedding their code within SVG files, threat actors can infiltrate networks and bypass conventional defenses that are tuned primarily to detect binary files or known script patterns. The encoded payload is manipulated in such a way that conventional static analysis tools are rendered ineffective. Instead of being flagged by static rulesets, the payload requires dynamic analysis techniques. Through incremental tweaks to the Base64 encoding process, attackers ensure that each malicious file may exhibit unique characteristics, thereby evading heuristic detection mechanisms. This subtle, yet advanced technique exemplifies the adaptive nature of modern cyber threats, where even minor variations can differentiate legitimate traffic from nefarious actions.

Further complicating the detection process, the SVG files incorporate obfuscated script markers and URL redirection patterns embedded within the encoded strings. When a vulnerable web browser processes these files, the embedded strings are decoded in real-time, dynamically generating HTML content that directs unsuspecting users to counterfeit login or verification pages. This process capitalizes on the inherent trust placed in SVG files as a static, benign medium. However, by exploiting the rendering behavior of modern web engines, threat actors are able to create interactive phishing environments on the fly. The chain of exploitation does not rely on traditional exploits of software vulnerabilities or overt malicious code. Instead, it leverages the trusted file format and the Base64 encoding method to create an invisible bridge between presentation and attack. The result is a sophisticated phishing mechanism that is both stealthy and highly effective in breaching established security perimeters.

The tactics and techniques observed here have significant overlap with frameworks such as MITRE ATT&CK. Attackers exhibit behaviors that align with MITRE ATT&CK tactics T1566, which involves phishing, and T1027, which pertains to obfuscated files and information. In this context, Base64 encoding is not merely a method for protecting data integrity or transmission; it has been repurposed as a tool for stealth. The deliberate use of this encoding within SVG files demonstrates an understanding of both the technical and procedural vulnerabilities inherent in modern cybersecurity frameworks. Security teams are therefore encouraged to extend their analysis routines beyond conventional file types. Adapting detection rules that account for hidden anomalies in vector graphics is paramount, as these SVG files, when analyzed in isolation, appear legitimate while in coordinated cyber campaigns they serve as gateways for sophisticated phishing attacks.

The intricacies of this approach are further underlined by the method of dynamic evaluation employed by the malicious files. Traditional antivirus solutions rely heavily on static signature matching. However, the embedded Base64 payload necessitates dynamic analysis or behavioral monitoring. When static scanning methods are applied to these SVG files, the encoded content is often skipped or misinterpreted, leading to potential bypass of traditional defenses. It is essential for organizations to integrate dynamic sandbox environments that replicate the file’s execution process, thereby allowing cybersecurity personnel to observe and detect abnormal file behavior. The dynamic analysis should include deobfuscation of embedded strings, real-time decoding of Base64 content, and monitoring of the resultant behavior to flag anomalous interactions with system resources or network communications.

From a strategic standpoint, the evolution of phishing techniques targeting trusted web file formats underlines a shift in adversary tactics. Historically, phishing was predominantly associated with email campaigns that targeted users with malicious links or attachments. In the current landscape, however, threat actors are pivoting towards the exploitation of familiar, benign file formats such as SVGs. The adoption of this method not only broadens the scope of potential attack vectors but also increases the difficulty of detection. The reliance on trusted file formats means that even advanced security tools may overlook these threats unless specifically configured to analyze dynamic file behavior. Therefore, it is critical to reassess current security protocols and to expand the range of data inputs subjected to rigorous dynamic analysis.

The use of SVG files as a delivery mechanism for phishing payloads has significant implications for both endpoint security and web application integrity. For endpoints, the challenge lies in monitoring and intercepting seemingly normal file activity that occurs during routine browsing. For web applications, the integration of dynamic content delivered via seemingly standard SVG files can introduce untrusted behavior, potentially leading to unauthorized data capture or credential theft. Security professionals must, therefore, invest in enhanced threat intelligence and incorporate layered defense mechanisms that include robust dynamic file scanning, deeper inspection of non-traditional file formats, and continuous monitoring of system anomalies.

The investigative findings underscore the significance of an integrated approach that combines static and dynamic security measures. The dynamic aspect, provided by sandboxing environments, should be well aligned with static analysis tools to ensure a comprehensive security posture. As threat actors constantly adjust their methods to avoid detection, the necessity for continuous adaptation of cybersecurity measures becomes evident. In this scenario, automated threat intelligence feeds, cross-platform collaboration, and real-time updates to intrusion detection systems are critical components in the fight against these evolving threats. In addition to technical countermeasures, user education is a vital line of defense. Training end-users to recognize the subtle signs of phishing attacks, even when delivered in unconventional formats, can dramatically reduce the incidence of successful social engineering attacks. Increased awareness among both IT personnel and general users is necessary to safeguard against the exploitation of trusted file formats.

The transition to these new sophisticated attack techniques presents challenges that extend beyond traditional cybersecurity measures. As illustrated in this report detailing the exploitation of 44 SVG files, the sophistication of today's threat landscape is underpinned by the attackers' ability to dynamically alter attack vectors with minimal observable changes. To effectively counter these threats, security organizations must leverage integrated platforms that combine real-time threat intelligence with advanced behavioral analytics. It is only through such holistic approaches that the detection and mitigation of these covert phishing attacks can be achieved. Moreover, the continuous evolution of such tactics highlights the need for an agile response framework that encompasses routine threat hunting exercises, frequent security audits, and the updating of incident response protocols to address not only known threats but also emerging adversarial techniques.

As organizations work to fortify their cybersecurity defenses, the importance of collaboration with industry groups and threat intelligence communities cannot be overemphasized. By sharing observed patterns and indicators of compromise across sectors, cybersecurity professionals can benefit from a broader, more comprehensive perspective on evolving attack trends. Such an approach is essential for building layered defenses that are both adaptive and resilient. The insights gained from these shared experiences contribute to an overall strengthened posture against the dynamic and elusive methods employed by threat actors. Companies and government agencies alike must recognize that even subtle changes in file behavior can herald significant underlying threats, warranting proactive and sustained vigilance.

References

The analytical foundation of this report rests on comprehensive research and cross-verification with multiple trusted sources. The initial identification and subsequent verification of the SVG exploitation technique were primarily based on findings from VirusTotal, whose advanced detection capabilities brought to light the stealthy nature of the attack vector. Additional corroboration was obtained from the National Vulnerability Database (NVD), renowned for its extensive repository of technical vulnerabilities, as well as insights gleaned from community discussions on platforms such as LinkedIn and Reddit. Furthermore, independent research publications and vendor advisories have contributed to the validation of these findings, ensuring that the information presented is both current and actionable. These sources collectively underscore the urgency of adapting existing security measures to encompass not only traditional threats but also emerging vectors that exploit trusted file formats.

Rescana is here for you

At Rescana, we understand that the security landscape is continually evolving, and emerging threat vectors require a multifaceted, dynamic response. Our commitment to delivering cutting-edge intelligence and innovative solutions is exemplified by our proactive approach to Third Party Risk Management. We continuously integrate advanced detection tools and dynamic behavioral analysis into our platform to support our customers in identifying and mitigating risks before they escalate into substantial vulnerabilities. The tactics highlighted in this report illustrate not only the sophistication of modern cyber adversaries but also reaffirm our mission to equip organizations with the insights and technology necessary to stay one step ahead. Our team is dedicated to ensuring that your digital assets remain secure, and we are here to help you adapt to the ever-changing threat environment.

We believe that fostering robust, adaptive defenses requires a combination of advanced analytical tools, real-time threat intelligence, and comprehensive user education. Our expert research team continually monitors developments across the global cybersecurity landscape, translating complex technical details into actionable intelligence that supports informed decision-making. Through ongoing collaboration and active threat sharing, Rescana remains committed to providing its customers with the tools they need to reinforce their security posture. We are here for you, and we welcome any questions or requests for further details regarding this advisory report. Please do not hesitate to reach out to our team at ops@rescana.com as we work together to create a secure digital future.