KSeF token disclosure via predictable custom encoding
Published Mar 12, 2026 · Updated Mar 12, 2026
Weak token encoding in Streamsoft Prestiż 12.2.363.17 through 20.0.380.91 allows remote attackers to guess a KSeF token. The custom encoder exposes a repeatable relationship between known KSeF token values and their encodings, enabling prediction of an unknown token; CERT Polska does not disclose the algorithm or code locus. Exploitation requires analysis of encodings for known token values and compromises the confidentiality of the guessed token, with no reported data modification or service interruption.
Summary
What happened
Weak token encoding in Streamsoft Prestiż 12.2.363.17 through 20.0.380.91 allows remote attackers to guess a KSeF token. The custom encoder exposes a repeatable relationship between known KSeF token values and their encodings, enabling prediction of an unknown token; CERT Polska does not disclose the algorithm or code locus. Exploitation requires analysis of encodings for known token values and compromises the confidentiality of the guessed token, with no reported data modification or service interruption.
The record
- CVE
- CVE-2026-0809
- Published
- Mar 12, 2026
- Updated
- Mar 12, 2026
- Vendor
- Streamsoft
- Product
- Streamsoft Prestiż
- Classifications
- CWE-261, CAPEC-55, T1528
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 12, 2026CVE publishedPublication date reported by the CVE source.
- Mar 12, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=12.2.363.17 <20.0.380.92
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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