Mythic EUVD-2026-114241

Exploitation requires the attacker to already control the files on a target endpoint where a Mythic agent operates, and to place attacker-controlled HTML inside a file named with a .pdf extension; the payload only executes when a Mythic operator downloads that file and actively clicks Preview Media, at which point /direct/view content-sniffs the file and renders it as HTML in the Mythic UI origin. Key limiting factors: the attacker needs prior control of agent-reachable endpoint files (a privileged position in the engagement), the operator must perform the download-and-preview interaction (UI:A), and the attack depends on the browser content-sniffing an HTML body out of a .pdf-named file (reflected as AT:P). Affected versions are Mythic 3.2.16 through 3.4.0.61; updating to the patched version is the fix.

This is a stored XSS (CWE-79) in the Mythic C2 framework's React UI, scored CVSS 4.0 7.4 (High). The 4.0 vector (AV:N/AC:L/AT:P/PR:N/UI:A) shows a network-reachable flaw with low complexity but two real brakes: AT:P (a specific attack requirement - the browser's content-sniffing of an HTML payload planted in a .pdf-named file via /direct/view) and UI:A (an operator must actively download the file and click Preview Media). Impact is high to confidentiality and integrity of the Mythic system (VC:H/VI:H) because rendering same-origin HTML can steal localStorage JWTs, yielding full GraphQL and REST access; VA:N and all subsequent-system metrics are N. No EPSS score and no KEV status are present in the input, so widespread or active exploitation cannot be asserted - exploitation here is inherently targeted, requiring an attacker to already control files on an endpoint a Mythic agent has compromised and to rely on operator interaction, so this reads as a plausible targeted operator-compromise risk rather than a mass-exploited internet threat. A public PoC reference (h00die/mythic_xss) is listed but is not confirmed as working exploit code. The vendor priority label is this_week, which aligns with a patched, High-severity but interaction- and position-gated bug rather than an emergency.

An attacker who has compromised an endpoint running a Mythic agent plants attacker-controlled HTML/JavaScript inside a file given a .pdf name, so that when the operator later downloads that file and clicks Preview Media, /direct/view content-sniffs and renders it as HTML in the Mythic UI origin. The injected script reads the operator's JWTs from localStorage, granting the attacker full GraphQL and REST API access to the Mythic server. A public PoC reference exists but is not verified as working exploit code, and success depends on the operator performing the preview action (UI:A).