CVE-2026-0809Weak KSeF token encoding in Streamsoft Prestiż

Description

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.

Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.

Affected products and versions

References and patches

• https://www.streamsoft.pl/streamsoft-prestiz/ product
• https://cert.pl/posts/2026/03/CVE-2026-0809 third-party-advisory