CVE-2026-0809 in Prestiż
Summary
by MITRE • 03/12/2026
Use of a custom token encoding algorithm in Streamsoft Prestiż software allows the value of the KSeF (Krajowy System e-Faktur) token to be guessed after analyzing how tokens with know values are encoded.
This issue was fixed in version 20.0.380.92.
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Analysis
by VulDB Data Team • 03/17/2026
The vulnerability identified as CVE-2026-0809 represents a critical cryptographic weakness in the Streamsoft Prestiż software ecosystem, specifically affecting the Krajowy System e-Faktur (KSeF) token management system. This flaw resides in the implementation of a custom token encoding algorithm that deviates from established cryptographic standards and best practices. The software's proprietary encoding mechanism fails to provide adequate entropy and randomness, creating predictable patterns that can be exploited by malicious actors to infer the values of sensitive authentication tokens. The vulnerability directly impacts the security posture of Polish electronic invoicing infrastructure, where KSeF tokens serve as critical authentication credentials for accessing government-mandated digital invoice processing systems.
The technical exploitation of this vulnerability stems from the predictable nature of the custom encoding algorithm, which allows attackers to perform pattern analysis on known token values to deduce the encoding methodology. This approach constitutes a classic cryptographic weakness where the custom implementation lacks proper randomization and cryptographic strength, making it susceptible to statistical analysis and reverse engineering. The flaw enables attackers to potentially reconstruct valid tokens without possessing the original private keys or authentication credentials, thereby compromising the entire token-based authentication framework. This vulnerability aligns with CWE-330, which addresses the use of insufficiently random values, and represents a significant deviation from established security protocols that require cryptographically secure random number generation for token creation and validation.
The operational impact of CVE-2026-0809 extends beyond simple authentication bypass, as it fundamentally undermines the integrity of the KSeF system and creates opportunities for unauthorized access to sensitive financial data. Organizations utilizing Streamsoft Prestiż software for electronic invoicing face potential exposure to fraudulent invoice processing, unauthorized financial transactions, and data breaches that could compromise their compliance with Polish tax regulations and international data protection standards. The vulnerability affects not only the immediate security of individual tokens but also creates cascading risks where compromised tokens could be used to access multiple systems or services within the same organizational infrastructure. This risk is particularly concerning given the regulatory requirements and audit trails associated with electronic invoicing systems, where unauthorized access could lead to significant financial and legal consequences.
The remediation of this vulnerability required the implementation of a proper cryptographic token encoding mechanism that adheres to established security standards and best practices. Version 20.0.380.92 of Streamsoft Prestiż software addresses the issue by replacing the custom encoding algorithm with a standardized approach that incorporates cryptographically secure random number generation and proper token entropy. This fix aligns with ATT&CK technique T1552.001, which focuses on credentials from password storage components, and demonstrates the importance of proper cryptographic implementation in security-critical systems. Organizations should prioritize immediate deployment of this update while also conducting comprehensive security assessments of their token management systems to identify potential vulnerabilities in other custom cryptographic implementations. The incident serves as a critical reminder of the dangers associated with proprietary cryptographic solutions and the necessity of adhering to established security frameworks such as NIST guidelines for cryptographic key management and token-based authentication systems.