XSS in Gchq Cyberchef

CVE-2026-42615

GCHQ CyberChef before 11.0.0 allows XSS via Show Base64 offsets, as demonstrated by the /#recipe=Show_Base64_offsets('%3Cscript substring.

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.000 (2.8th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.2 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N.

Affected products

Gchq Cyberchef — versions 0

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

Frequently asked questions

What is CVE-2026-42615?: CVE-2026-42615 is a high-severity vulnerability in Gchq Cyberchef, classified under Cross-site Scripting. CVSS score: 7.2/10. Published 2026-04-29.
How severe is CVE-2026-42615?: High severity. CVSS v3 base score is 7.2 out of 10.