What is CVE-2026-26378?

CVE-2026-26378 is a medium-severity vulnerability in Koha, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-06-03.

How severe is CVE-2026-26378?

Medium severity. CVSS v3 base score is 5.4 out of 10.

XSS in Koha

CVE-2026-26378

Cross Site Scripting vulnerability in Koha 25.11 and before allows a remote attacker to execute arbitrary code via file upload function in Invoice features

Vulnerability class: XSS (Cross-Site Scripting)

Published 2026-06-03 · last modified 2026-07-22.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.005 (37.0th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 37th percentile — 37.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002

Affected products

Koha

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/Koha-Community/Koha (Product)
g03m0n.github.io (Third Party Advisory)
g03m0n.github.io/posts/cve-2026-26378/ (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2026-26378?: CVE-2026-26378 is a medium-severity vulnerability in Koha, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-06-03.
How severe is CVE-2026-26378?: Medium severity. CVSS v3 base score is 5.4 out of 10.