TinaCMS CLI CVE-2026-63123

Two specific conditions must both be met: (1) the target developer must be running tinacms dev locally - this vulnerability is exclusive to the CLI development server and is not present in production TinaCMS deployments; and (2) the developer must visit an attacker-controlled web page in the same browser session while the dev server is active, at which point the attacker page autonomously triggers the upload with no further developer interaction beyond the initial page visit (CVSS UI:R). The attack is bounded to writing files within the configured media root directory - the resolveStrictlyWithinBase path sanitization function prevents traversal to other filesystem locations, which limits the attacker to poisoning or overwriting content within that directory. No authentication layer exists on the dev server (PR:N), so no credential theft is a prerequisite. The vulnerability does not apply to developers who run tinacms dev exclusively in isolated browser profiles or network namespaces, or who have upgraded to 2.5.2.

The CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N, score 6.5) accurately characterizes the attack: network-reachable, low complexity, no authentication required, but gated on developer user interaction (visiting a malicious page). Real-world risk is meaningful but contextually bounded - this vulnerability exists only in the development server (tinacms dev) and does not affect production deployments, substantially limiting the at-risk population to developers actively editing TinaCMS projects locally. The integrity impact is high within the media root but is hard-bounded by resolveStrictlyWithinBase path sanitization; the researcher explicitly did not demonstrate traversal outside the media directory or code execution, so the 'H' integrity rating reflects the worst-case file-write scenario rather than RCE. No KEV listing exists, meaning active exploitation is not confirmed by CISA. A researcher-validated POC exists in the GHSA advisory, confirming exploitability. EPSS data is not provided in the input. The overall priority is moderate: developers using @tinacms/cli < 2.5.2 should upgrade promptly, but the constrained impact surface and UI:R requirement reduce urgency relative to server-side CSRF vulnerabilities.

An attacker sends a developer a phishing link to a malicious web page containing JavaScript that constructs a multipart/form-data POST to http://localhost:<tinacms-port>/media/upload/injected-asset.jpg with attacker-supplied file contents. When the developer opens the link while tinacms dev is running, the browser submits the simple cross-origin request without a preflight check; the dev server processes the upload and writes the attacker's content to the media root. A researcher-validated POC for this exact scenario is included in GHSA-rgr9-r7mj-mf6x, confirming that the file write completes even though the browser treats the fetch response as blocked.