EUVD-2026-42294Severity by source
AV:L/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CyberChef is commonly accessed as a hosted web application with shareable recipes, making AV:N more representative of realistic delivery; all other metrics align with the XSS impact model and mandatory user interaction.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
2DescriptionCVE.org
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.
AnalysisAI
Prototype pollution in CyberChef prior to 11.2.0 enables cross-site scripting via a chained operation attack. The Series Chart operation accepts __proto__ as a valid CSV key without sanitization, corrupting the JavaScript Object prototype; when downstream operations such as Parse UDP generate HTML output, the polluted prototype injects attacker-controlled JavaScript that executes in the victim's browser. The vendor has released a fix in version 11.2.0; no public exploit and no CISA KEV listing have been identified at time of analysis.
Technical ContextAI
CyberChef (cpe:2.3:a:gchq:cyberchef:*:*:*:*:*:*:*:*) is a browser-based data transformation toolkit developed by GCHQ for cryptographic, encoding, compression, and analysis operations. The root cause is CWE-79 (Improper Neutralization of Input During Web Page Generation / XSS), with the triggering mechanism being prototype pollution: the Series Chart operation's CSV parser fails to reject the reserved JavaScript property key __proto__, which when set modifies properties on the global Object prototype shared across all JavaScript objects in the page. This polluted prototype is then read by other operations - specifically those that generate HTML output such as Parse UDP - causing arbitrary attacker-supplied values to be embedded as executable script content in the rendered output. Prototype pollution as an XSS vector is a well-documented attack pattern in JavaScript runtimes where object merging or structured-data parsers (CSV, JSON) do not block prototype-chain keys.
RemediationAI
Upgrade to CyberChef version 11.2.0 or later, which contains the fix committed in 85db3be5d0096859b810f0e8d3e151d5dc9b948f and merged via pull request #2569 (https://github.com/gchq/CyberChef/pull/2569). The patched release is available at https://github.com/gchq/CyberChef/releases/tag/v11.2.0. Organizations hosting CyberChef internally should redeploy from the updated build immediately. If immediate upgrade is not feasible, operators should restrict the processing of externally supplied CSV files through the Series Chart operation to trusted internal sources only, and should avoid constructing recipes that chain Series Chart with HTML-generating operations such as Parse UDP on untrusted input until the patch is applied. No adverse side effects of the patch have been reported.
CyberChef before 8.31.2 allows XSS in core/operations/TextEncodingBruteForce.mjs. Rated medium severity (CVSS 6.1), this
Cross-site scripting in GCHQ CyberChef before 11.0.0 allows attackers to execute arbitrary JavaScript in a victim's brow
Same weakness CWE-79 – Cross-site Scripting (XSS)
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External POC / Exploit Code
Leaving vuln.today