XSS in Gchq Cyberchef
CVE-2026-57439
CyberChef is a web app for encryption, encoding, compression, and data analysis. Prior to 11.2.0, the Series Chart operation accepts __proto__ as a key while parsing user-supplied CSV, allowing prototype pollution that can be chained with operations such as Parse UDP to inject malicious JavaScript into HTML output. This issue is fixed in version 11.2.0.
Vulnerability class: XSS (Cross-Site Scripting)
EPSS: 0.001 (0.7th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.0 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
Affected products
- Gchq Cyberchef — versions < 11.2.0
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
- security-advisories@github.com (x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-57439?
- CVE-2026-57439 is a medium-severity vulnerability in Gchq Cyberchef, classified under Cross-site Scripting. CVSS score: 5.0/10. Published 2026-07-08.
- How severe is CVE-2026-57439?
- Medium severity. CVSS v3 base score is 5.0 out of 10.