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The vulnerability stems from improper handling of user-controlled input within the TinaCMS CLI package.
Specifically, during the build or code generation pipeline, environment variables and Git references are read.
Sources such as VERCEL_GIT_COMMIT_REF, GITHUB_BRANCH, or HEAD are captured directly as branch strings.
These raw strings are concatenated into the API URL construction without any sanitization or encoding.
Functions like _createApiUrl append the branch value directly into the target endpoint string path segment.
No encodeURIComponent, JSON.stringify, or string-escape mechanism is applied anywhere along this path.
Consequently, the genClient template function interpolates this unsanitized API URL directly into source templates.
The resulting generated client.ts file contains the raw interpolated URL enclosed inside single or double quotes.
An attacker capable of controlling the Git branch name can craft a malicious, git-valid branch identifier.
By embedding a single quote character within the branch name, the attacker prematurely closes the string literal.
Following the closing quote, arbitrary JavaScript expressions can be appended using standard expression syntax.
A trailing quote or operator reopens a string literal to maintain valid syntax and prevent build errors.
When the consumer build process runs, it compiles and evaluates the generated TypeScript or JavaScript module.
Because the injected expression is executed at module top level during evaluation, it runs with full privileges.
This leads directly to build-time arbitrary code execution in the context of the consumer build environment.
Typical preview deployments on platforms like Vercel or GitHub Actions automatically trigger builds on pull requests.
An attacker opening a pull request with a malicious branch name forces the runner to execute their payload.
Sensitive build environment variables, including provider secrets and tokens, become instantly accessible.
Furthermore, build artifacts can be modified, facilitating supply-chain compromise of the deployed outputs.
Network access from the runner enables potential data exfiltration to external attacker-controlled servers.
Similarly, related legacy code paths like Forestry YAML migration templates suffered from analogous flaws.
In those cases, unquoted markers allowed unescaped configuration labels to achieve identical RCE results.
Remediation requires strict input sanitization, encoding, and the adoption of safe serialization methods.
Developers must apply JSON.stringify or encodeURIComponent to all runtime values injected into code templates.
Alternatively, passing configuration values through external JSON config files prevents code injection entirely.
Upgrading affected CLI packages ensures robust defenses against branch and configuration-based injections.
Security audits of build-time code generators remain critical for preventing similar template injection vectors.
Proper parsing safeguards protect developer environments from malicious code execution during automated builds.
Maintaining strict separation between code structure and dynamic configuration data is paramount for security.
DailyCVE Form:
Platform: TinaCMS CLI
Version: Prior to 2.4.3
Vulnerability : Code Injection
Severity: High
date: June 19, 2026
Prediction: Patched in 2.4.3
What Undercode Say:
mkdir /tmp/tinacms-repro && cd /tmp/tinacms-repro git init && git commit --allow-empty -m "init" git branch "x'+(globalThis.__TINA_PROBE='hit')+'" npm init -y && npm install esbuild
import { transform } from 'esbuild';
import vm from 'vm';
const branch = "x'+(globalThis.__TINA_PROBE='hit')+'";
const apiURL = `https://content.tinajs.io/2.4/content/my-client/github/${branch}`;
const generated = `
import { createClient } from "tinacms/dist/client";
export const client = createClient({ url: '${apiURL}', token: 'xxx' });
`;
const compiled = await transform(generated, { loader: 'ts', format: 'cjs' });
const sandbox = {
globalThis: {},
module: { exports: {} },
exports: {},
require: () => ({ createClient: (o) => o }),
};
vm.createContext(sandbox);
vm.runInContext(compiled.code, sandbox);
console.log("__TINA_PROBE =", sandbox.globalThis.__TINA_PROBE);
Exploit: (Educational Purposes!)
The exploit leverages Git branch naming flexibility where `git check-ref-formatpermits single quotes and mathematical or string concatenation characters. By crafting a branch name such asx’+(globalThis.__TINA_PROBE=’hit’)+, an attacker ensures that when the TinaCMS CLI generatesclient.ts, the unescaped branch variable breaks out of the string literal contexturl: ‘${apiURL}’`. The single quote closes the string, the injected JavaScript executes arbitrary code during module evaluation, and the trailing operator reopens a string to preserve syntax correctness so the build does not fail outright before execution.
Protection: from this CVE
Use JSON.stringify(value) to safely serialize any runtime value interpolated into generated source templates.
Apply encodeURIComponent() to the branch value before constructing the API URL path segment.
Apply the same treatment to apiURL, token, errorPolicy, cacheDir, and code generation templates.
Move runtime values out of source templates entirely by passing them through a JSON config file that the generated client reads at runtime.
Update @tinacms/cli to version 2.4.3 or later.
Impact:
The injected expression executes with the full privileges of the consumer build process. In typical Vercel or GitHub Actions preview deployments:
Build environment variables are accessible via process.env, including NPM_TOKEN, VERCEL_TOKEN, cloud provider secrets, and API keys.
Build artifacts can be modified, enabling supply-chain compromise of the deployed output.
Network access is available to exfiltrate sensitive data to external servers.
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Sources:
Reported By: github.com
Extra Source Hub:
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