CVE-2026-110652 in DocumentServer
Summary
by MITRE • 10/15/2026
ONLYOFFICE DocumentServer before 10.0.0 contains an unauthenticated server-side request forgery vulnerability in the /downloadfile/:docid endpoint that allows remote attackers to bypass the private-IP request-filtering-agent by exploiting the isInJwtToken flag when JWT verification is disabled in the default configuration. Attackers can submit a crafted request body containing an internal or loopback URL, which is treated as a DIRECT request skipping private-address filtering, causing the server to fetch and proxy back arbitrary private-network and cloud metadata content.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in ONLYOFFICE DocumentServer prior to version 10.0.0 represents a critical security flaw rooted in improper input validation and logic errors within the document download mechanism. Specifically, this unauthenticated server-side request forgery (SSRF) targets the /downloadfile/:docid endpoint, which is designed to retrieve documents from various sources for viewing or editing by users. The core of the issue lies in how the application handles JWT verification settings during default configurations. When JWT verification is disabled, a specific flag known as isInJwtToken becomes relevant to determining whether an incoming request should be subject to strict private IP filtering rules. This architectural decision creates a bypass vector where attackers can manipulate the request context to evade security controls intended to restrict outbound connections to internal or loopback addresses.
From a technical perspective, the flaw exploits the conditional logic governing network requests initiated by the server itself. The application employs a private-IP request-filtering-agent designed to prevent SSRF attacks by blocking attempts to access local services such as cloud metadata endpoints (e.g., AWS EC2 instance metadata service at 169.254.169.254) or internal network resources. However, when the isInJwtToken flag is set in a manner that indicates the request originates from within a trusted JWT context, and JWT verification is disabled globally, the system incorrectly classifies these requests as direct local operations rather than external fetches requiring filtering. Consequently, the server proceeds to make HTTP requests to arbitrary URLs provided by the attacker without applying the necessary IP address restrictions. This allows remote attackers to craft malicious request bodies containing internal or loopback URLs that are processed and proxied back to the client, effectively bypassing the intended security boundary.
The operational impact of this vulnerability is severe due to its unauthenticated nature and potential for data exfiltration. Attackers do not need valid credentials to exploit this flaw, making it accessible to any internet-facing instance running a vulnerable version with default settings. By leveraging this SSRF capability, adversaries can access sensitive internal services that are typically isolated from public networks. A primary target is cloud metadata endpoints, which often contain temporary security credentials, IAM role information, and other configuration details critical for maintaining the integrity of cloud infrastructure. Compromise of these resources could lead to unauthorized access to storage buckets, database instances, or compute engines within a private network. Furthermore, internal services such as administrative panels, monitoring tools, or legacy applications running on loopback interfaces become exposed, potentially leading to further lateral movement and deeper penetration into the organization's IT environment.
This vulnerability aligns with CWE-918, which describes Server-Side Request Forgery (SSRF) flaws where a web server makes requests based on user-supplied data without proper validation of the destination address. Additionally, it maps to MITRE ATT&CK technique T1502, specifically Subservice Discovery via Cloud Metadata APIs, as attackers can use this flaw to enumerate and access cloud provider metadata services that are not directly accessible from the public internet. The exploitation path also reflects CWE-798, involving the use of hardcoded or default credentials/settings that weaken security posture by disabling authentication mechanisms like JWT verification while retaining complex logic paths that may contain bypasses.
To mitigate this risk, organizations running ONLYOFFICE DocumentServer must immediately upgrade to version 10.0.0 or later, where these logical flaws have been addressed in the request handling and filtering agents. For environments unable to patch immediately due to compatibility constraints, it is imperative to ensure that JWT verification remains enabled even if custom token validation logic is required, as disabling this feature exposes the application to such bypasses. Network-level mitigations should also be implemented by configuring firewalls or reverse proxies to block outbound connections from the DocumentServer host to private IP ranges and cloud metadata endpoints unless explicitly required for business operations. Regular security audits of configuration settings are essential to ensure that default configurations do not inadvertently disable critical authentication controls, thereby maintaining a robust defense-in-depth strategy against SSRF attacks.