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High, CVSS 7.2

Document Merge Service vulnerable to RCE via SSTI (xlsx tempaltes)

CVE-2026-53964GHSA-w47q-945m-q9pc

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (document-merge-service 9.1.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.2 · CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
EPSS
  • CVE-2026-53964: 0.49% estimated exploitation activity in the next 30 days; percentile 42.37 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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 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

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-w47q-945m-q9pc

Agent brief

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# Patch Next advisory brief: CVE-2026-53964

Advisory: Document Merge Service vulnerable to RCE via SSTI (xlsx tempaltes)
IDs: CVE-2026-53964, GHSA-w47q-945m-q9pc
Record: https://patchnext.com/advisories/cve-2026-53964 (revision 1, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: document-merge-service 9.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI document-merge-service: affected < 9.1.0; fixed in 9.1.0

## Suggested inspection (read-only)
- `python -m pip show document-merge-service`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on document-merge-service.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w47q-945m-q9pc (GitHub-reviewed advisory GHSA-w47q-945m-q9pc lists affected ranges: PyPI document-merge-service >=0 <9.1.0)

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