CVE-2026-0809 Weak KSeF token encoding in Streamsoft Prestiż
Weak custom token encoding in Streamsoft Prestiż allows attackers to guess KSeF tokens, potentially bypassing authentication or taking over accounts.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-0809?
CVE-2026-0809 is a medium-severity vulnerability in Streamsoft Prestiż, published on 12 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-261
Which versions are affected by CVE-2026-0809?
How do I fix CVE-2026-0809?
No fix has been published for CVE-2026-0809 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-0809 being exploited?
There is no known exploitation of CVE-2026-0809 in the wild and no public exploit code.
Sources
Also known as GHSA-4h75-v39v-9pq7.