External risk intelligence

ONLYOFFICE DocumentServer Use-After-Free Vulnerability Allows Code Execution.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2023-30186

ONLYOFFICE DocumentServer is commonly deployed as a web-based document editing and collaboration platform. Such services are typically exposed to the internet or to broad internal user networks to allow remote access to document processing and collaboration features, making the application's interface a likely point of public or external network exposure.

Use After Free

Onlyoffice Document Server

4.0.3 to 7.3.2

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability exists in ONLYOFFICE DocumentServer that could allow remote attackers to execute arbitrary code by tricking users into opening a specially crafted JavaScript file. This issue stems from a "use after free" defect within the software's handling of document rendering. The potential for code execution means this vulnerability could be leveraged to compromise systems if not addressed.

Software can be tricked to run unknown code.
Critical flaw could allow system compromise.
Confirm relevance and exposure to ONLYOFFICE DocumentServer.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending a specially crafted JavaScript file to a vulnerable ONLYOFFICE DocumentServer. This could allow them to execute arbitrary code on the server, potentially leading to a full system compromise.

No authentication needed to access.
Triggered by a malicious JavaScript file.
Allows arbitrary code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in ONLYOFFICE DocumentServer could allow an unauthenticated remote attacker to execute arbitrary code by tricking a user into opening a specially crafted JavaScript file. The attacker could potentially gain control over the server's processes, impacting its availability and integrity.

Server code execution.
Via crafted JavaScript file.
System compromise and data access.

Operational Fix

Recommended remediation, mitigation, and detection steps

System owners and infrastructure teams are likely responsible for addressing this critical vulnerability in ONLYOFFICE DocumentServer, which allows remote code execution via crafted JavaScript files. The first practical step is to identify all instances of the affected software, confirm their network exposure and business criticality, and locate the accountable owner. Subsequently, a risk-based remediation plan should be developed, potentially involving vendor coordination or temporary risk reduction measures while maintaining service availability.

Own the issue and asset inventory.
Verify external reachability and business impact.
Plan and coordinate remediation efforts.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is ONLYOFFICE DocumentServer?

ONLYOFFICE DocumentServer is a collaborative web-based suite used for editing and processing documents, spreadsheets, and presentations. It serves as a backend engine that allows teams to work on files simultaneously within a browser or integrated platforms. Because it handles complex document rendering tasks, it must process various file formats and scripts, which makes its internal handling of these data structures a critical function for security.

What does use-after-free mean in CVE-2023-30186?

This is a memory management flaw classified as CWE-416. It occurs when software continues to use a pointer to a memory location after that memory has been cleared or freed. In this specific CVE, if the software is tricked into accessing this stale memory space, an attacker can manipulate the process to run their own unauthorized instructions, leading to remote code execution.

How is this vulnerability triggered?

The vulnerability is triggered when the server processes a specially crafted JavaScript file. The flaw exists within the document rendering logic; standard, legitimate files used for routine document collaboration do not trigger this defect. The issue requires the application to attempt to render a malicious file designed to exploit the specific memory handling weakness during the rendering process.

Why is this CVE relevant to my network?

Halo Surface Signal notes that DocumentServer is often deployed to support remote collaboration, making it a likely candidate for network exposure. If your instance is internet-facing, it is accessible to unauthenticated remote parties. Even in internal networks, the service is often widely accessible to users, increasing the risk if a malicious file is uploaded or shared within the environment.

What should I do to address this risk?

Begin by identifying every instance of DocumentServer running in your environment to establish a clear asset inventory. Confirm which instances are reachable over the network and determine their business criticality. Once mapped, coordinate with your technical teams to verify your current version against the affected range (4.0.3 through 7.3.2) and prepare to apply the necessary updates or risk mitigation steps provided by the vendor.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.