Vulnerability · Published Oct 1, 2026 · Assigned by GitHub_M
CVE-2026-53964Document Merge Service vulnerable to RCE via SSTI (xlsx tempaltes)
High 7.2
In plain English
A high-severity security flaw in document-merge-service from adfinis. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 43% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Document Merge Service is a document template merge service providing an API to manage templates and merge them with given data. Prior to version 9.1.0, a remote code execution (RCE) via server-side template injection (SSTI) allows for user supplied code to be executed in the server's context where it is executed as the document-merge-server user with the UID 901 thus giving an attacker considerable control over the container. The vulnerability is limited to XLSX templates, were the xltpl library uses a npn-sandboxed Jinja environment for the processing of the template. This issue has been patched in version 9.1.0.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| PyPI | document-merge-service | 9.1.0 | GHSA-w47q-945m-q9pc |
| PyPI | document-merge-service | 9.1.0 | PYSEC-2026-3830 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| adfinis | document-merge-service | < 9.1.0 |
Weakness: CWE-1336 · Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H