document-merge-service CVE-2026-53964
HIGH
GHSA-w47q-945m-q9pc
Severity by source
AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Network-reachable API with no user interaction, but PR:H because template upload requires high-privilege credentials; full C/I/A impact within container scope.
Primary rating from GitHub Advisory.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Lifecycle Timeline
3DescriptionGitHub Advisory
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
AnalysisAI
Remote code execution via server-side template injection (SSTI) in document-merge-service affects all versions before 9.1.0, exploitable by authenticated users with access to upload XLSX templates. The xltpl library processes XLSX templates through a non-sandboxed Jinja2 environment, allowing an attacker to embed Jinja2 expressions that execute arbitrary code server-side as the document-merge-server user (UID 901). …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the attacker to hold high-privilege access sufficient to upload XLSX templates to the document-merge-service API (CVSS PR:H). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 score of 7.2 (AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H) accurately reflects the high authentication requirement (PR:H), which is the primary risk limiter here. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An authenticated user with template-upload privileges submits a crafted XLSX file containing a Jinja2 SSTI payload (for example, referencing Python builtins via the class hierarchy) to the document-merge-service API. When the service processes the template using xltpl's non-sandboxed Jinja2 environment, the injected expression is evaluated, executing an OS command as UID 901 within the container. … |
| Remediation | The primary fix is to upgrade document-merge-service to v9.1.0 or later. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, inventory systems running document-merge-service versions prior to 9.1.0 and identify users with XLSX template upload permissions; immediately restrict this capability to essential personnel and implement mandatory approval workflows. …
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