CVE-2026-53964 — document-merge-service
HIGHCVE-2026-53964 is a high-severity (CVSS 7.2) CWE-1336 vulnerability in document-merge-service. A fix is available for document-merge-service — see the affected versions and patch details below.
Document Merge Service vulnerable to RCE via SSTI (xlsx tempaltes)
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-53964.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-53964 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 384,534 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
document-merge-serviceReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | document-merge-service | all versions | 9.1.0pip install --upgrade 'document-merge-service==9.1.0' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for document-merge-service, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update document-merge-service to 9.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53964 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-53964 in your dependencies?
Find it across PyPI, including transitive dependencies.