In the ever-evolving landscape of cybersecurity, a new and alarming vulnerability has emerged, casting a shadow over Grist-Core, the popular open-source, self-hosted relational spreadsheet-database. Dubbed “Cellbreak” by Cyera Research Labs, this critical flaw (CVE-2026-24002, CVSS score: 9.1) opens the door to remote code execution (RCE) attacks, transforming seemingly innocuous spreadsheet formulas into potent weapons for system compromise.
The “Cellbreak” Vulnerability Unveiled
The discovery, credited to security researcher Vladimir Tokarev, highlights a dangerous paradigm shift: “One malicious formula can turn a spreadsheet into a Remote Code Execution (RCE) beachhead,” Tokarev warned. This isn’t merely a data integrity issue; it’s a “sandbox escape” that blurs the lines between benign cell logic and hostile host execution, potentially allowing attackers to run operating system commands or execute host-runtime JavaScript.
A Deep Dive into Pyodide Sandbox Escape
At its core, Cellbreak is a Pyodide sandbox escape vulnerability, a category of flaw that recently impacted other platforms like n8n (CVE-2025-68668, aka N8scape). Grist-Core’s Python formula execution, designed to run untrusted formulas within the isolated environment of Pyodide – a Python distribution enabling browser-based execution via WebAssembly (WASM) – is the root cause. The intention was sound: to contain Python code within a secure sandbox. However, Grist’s reliance on a blocklist-style security approach proved to be its Achilles’ heel.
The Mechanics of Exploitation
Tokarev elaborated on the exploit’s mechanism: “The sandbox’s design allows traversal through Python’s class hierarchy and leaves ctypes available, which together open access to Emscripten runtime functions that should never be reachable from a formula cell.” This potent combination allows for the execution of host commands and JavaScript within the host runtime, granting attackers alarming capabilities such as filesystem access and the exposure of sensitive secrets.
Specifically, if a Grist instance has GRIST_SANDBOX_FLAVOR set to Pyodide and a user opens a malicious document, that document can be leveraged to execute arbitrary processes on the server hosting Grist. This means database credentials, API keys, and other critical data could be compromised, paving the way for further lateral movement within an organization’s network.
Grist’s Response and User Actions
Recognizing the severity of Cellbreak, Grist’s maintainers swiftly addressed the vulnerability in version 1.7.9, released on January 9, 2026. The primary fix involves moving Pyodide formula execution under the more secure Deno JavaScript runtime by default.
Immediate Steps for Users
Users are strongly urged to update to Grist version 1.7.9 or later without delay. To ascertain if your instance is affected, check the “sandboxing” section of your Grist Admin Panel. If “gvisor” is displayed, your instance is not vulnerable to this specific flaw. However, if “pyodide” is shown, an immediate update is crucial.
For those unable to update immediately, a temporary mitigation involves setting the GRIST_SANDBOX_FLAVOR environment variable to “gvisor.”
A critical caveat: while Deno is now the default for Pyodide formula execution, operators can explicitly revert to the less secure method by setting GRIST_PYODIDE_SKIP_DENO to “1.” This setting should be strictly avoided in any scenario where untrusted or semi-trusted formulas might be executed.
Beyond Grist: A Systemic Security Lesson
Tokarev’s insights extend beyond this specific vulnerability, offering a broader lesson in cybersecurity. “This mirrors the systemic risk found in other automation platforms: a single execution surface with privileged access can collapse organizational trust boundaries when its sandbox fails,” he stated. The Cellbreak findings underscore the imperative for sandboxing to be “capability-based and defense-in-depth, not a fragile blocklist.” The cost of neglecting robust security measures, as Tokarev aptly puts it, “is not just a bug — it is a data-plane breach.”
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