---
id: CVE-2026-53964
aliases:
  - GHSA-w47q-945m-q9pc
  - PYSEC-2026-3830
title: Document Merge Service vulnerable to RCE via SSTI (xlsx tempaltes)
summary: Document Merge Service vulnerable to RCE via SSTI (xlsx tempaltes)
severity: high
cvss: 7.2
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H'
vendor: document-merge-service
product: document-merge-service
ecosystem: pip
affected:
  - document-merge-service < 9.1.0
patched:
  - document-merge-service 9.1.0
published: '2026-08-19'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T12:25:55.406064842Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-w47q-945m-q9pc'
references:
  - url: >-
      https://github.com/adfinis/document-merge-service/security/advisories/GHSA-w47q-945m-q9pc
  - url: 'https://github.com/adfinis/document-merge-service'
  - url: 'https://github.com/adfinis/document-merge-service/releases/tag/v9.1.0'
  - url: 'https://pypi.org/project/document-merge-service'
  - url: 'https://github.com/advisories/GHSA-w47q-945m-q9pc'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-53964'
tags:
  - osv
  - pip
  - ghsa
cwe:
  - CWE-1336
ingestedAt: '2026-08-19T19:44:03.129Z'
---

## Overview

### Impact
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. 

### Patches
It has been patched in [v9.1.0](https://github.com/adfinis/document-merge-service/releases/tag/v9.1.0)

### Workarounds
Disable the upload/usage of XLSX templates.

### References
Are there any links users can visit to find out more?

https://book.hacktricks.xyz/pentesting-web/ssti-server-side-template-injection/jinja2-ssti

## Affected packages

- `document-merge-service < 9.1.0`

## Remediation

Upgrade to a patched release:

- `document-merge-service 9.1.0`