Summary
CyberChef: Prototype pollution in Series Chart operation
On 5 June 2026 CyberChef received a security vulnerability report from @hyuunnn detailing a vulnerability in the Series Chart operation, where malicious input could result in prototype pollution of the data structures outputted from the operation.
Other operations following Series Chart could have their behaviour manipulated by the attacker-controlled prototype, for example, injecting malicious content into their HTML output.
In this case, a demonstration was provided that chained the Series Chart operation with the Parse UDP operation to cause attacker controlled JavaScript to be executed.
Details
When the Series Chart operation parses user-supplied CSV, it accepts __proto__ as a key and uses it to pollute the object.
The objToTbale function in src/core/lib/Protocol.mjs, used in a number of IP parsing operations, renders data items within <td> tags without escaping.
These bugs can be chained to produce an XSS vulnerability.
Encoded input data is:
__proto__,<img src=x onerror=alert(document.domain)>,1
Workarounds
No workarounds are available. Users must upgrade to CyberChef v11.2.0.
Impact
Objects with attacker controlled prototypes could be processed by CyberChef operations. This enabled control of the output of some operations, and in particular, the ability to insert malicious JavaScript into the output of the Parse UDP operation.
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2026-57439 has a CVSS score of 5.0 (Medium). The vector is requires local access, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (11.2.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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This has been patched in release v11.2.0.
Frequently Asked Questions
- What is CVE-2026-57439? CVE-2026-57439 is a medium-severity cross-site scripting (XSS) vulnerability in cyberchef (npm), affecting versions < 11.2.0. It is fixed in 11.2.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2026-57439? CVE-2026-57439 has a CVSS score of 5.0 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of cyberchef are affected by CVE-2026-57439? cyberchef (npm) versions < 11.2.0 is affected.
- Is there a fix for CVE-2026-57439? Yes. CVE-2026-57439 is fixed in 11.2.0. Upgrade to this version or later.
- Is CVE-2026-57439 exploitable, and should I be worried? Whether CVE-2026-57439 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-57439 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-57439? Upgrade
cyberchefto 11.2.0 or later.