CyberChef EUVD-2026-55834

Exploitation requires that a victim user open a specifically crafted CyberChef URL containing a malformed #recipe= URL fragment with a large number of unmatched single-quote characters. The victim's browser must navigate to and begin loading the CyberChef application with this fragment present - either by clicking a shared link or via a redirect. This is a client-side-only vulnerability; server-side CyberChef deployments or API usage are not affected. The freeze is temporary and self-limiting: closing or killing the tab ends the condition. No authentication to any system is required (the parser runs before any login), but the attacker has no control over the victim's environment beyond inducing the URL visit. Non-default conditions are not required - any CyberChef instance prior to 11.3.0 processing a #recipe= fragment is vulnerable.

The CVSS 4.3 score and AV:N/AC:L/PR:N/UI:R vector accurately reflect the attack surface: any CyberChef user who opens a crafted URL is affected, but user interaction (UI:R) is a meaningful friction point. The Availability impact is rated Low (A:L), consistent with a browser-tab freeze that resolves when the tab is killed - not a persistent or cascading service disruption. EPSS data is not provided in the supplied intelligence, but given the client-side-only scope and the absence of KEV listing, real-world exploitation risk is likely low for most deployments. The tags in the supplied data list 'Privilege Escalation' and 'RCE', which are directly contradicted by the CVE description and should be treated as erroneous metadata - a misleading signal that could cause miscalibrated triage. The practical risk is context-dependent: for a security analyst using CyberChef in an air-gapped or isolated browser profile, this is negligible; for deployments where CyberChef is served as an internal web tool and users routinely process shared recipe URLs, the freeze-on-load behavior is a nuisance-level DoS. The fix is available and low-risk to apply. No evidence of active exploitation or public POC exists.

An attacker constructs a CyberChef URL with a #recipe= fragment containing thousands of consecutive unmatched single-quote characters (e.g., CyberChef/#recipe='''''....) and shares it via phishing email, Slack, or a malicious web page. When a security analyst clicks the link, their browser tab running CyberChef freezes during startup as the JavaScript engine exhaustively backtracks through the malformed input, disrupting their workflow for seconds or longer until the tab is manually killed. No public POC has been confirmed, but the attack payload is trivially constructable from the CVE description alone.