CVE-2026-109294 in Open WebUI
Summary
by MITRE • 10/12/2026
Open WebUI from 0.6.42 before 0.11.4 contains an uncontrolled resource consumption vulnerability that allows authenticated users to exhaust server memory by supplying compressed remote image URLs in chat messages. Attackers can point the image field at a host returning gzip-encoded responses, which get_image_base64_from_url decompresses unbounded, causing denial of service for all users.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability identified in Open WebUI versions prior to 0.11.4 represents a critical server-side resource exhaustion flaw rooted in the improper handling of compressed data streams during image processing operations. This issue specifically affects authenticated users who interact with the chat interface, allowing them to trigger excessive memory consumption on the backend server. The core technical failure lies within the function responsible for retrieving and converting remote images into base64 encoded strings, which fails to implement adequate bounds checking or size limits when decompressing gzip-encoded responses received from external hosts.
When a user submits a chat message containing an image field pointing to a maliciously crafted URL, the server initiates a request to fetch the resource at that location. If the remote host responds with data compressed using the gzip algorithm, the application attempts to decompress this payload entirely into memory before proceeding with further processing or storage. Because there is no mechanism in place to limit the size of the uncompressed output stream, an attacker can configure their server to return extremely large gzip-compressed files that expand significantly when decompressed. This unbounded decomposition causes the server process to allocate vast amounts of RAM rapidly, leading to a state where available memory resources are completely exhausted.
The operational impact of this vulnerability is severe, resulting in a denial-of-service condition for all users accessing the Open WebUI instance. As the application consumes increasing amounts of system memory to handle these malicious requests, it eventually reaches its resource limits and becomes unresponsive or crashes entirely. This disruption affects not only the attacker but also legitimate users who are unable to access the chat service during the period of resource exhaustion. The vulnerability effectively allows a single authenticated user to degrade or halt the availability of the entire platform by exploiting this inefficient memory management practice in image handling routines.
From a classification perspective, this flaw aligns with CWE-400, which describes uncontrolled resource consumption, and falls under the ATT&CK technique T1496, known as Resource Hijacking, where an adversary uses computing resources to disrupt service availability rather than stealing data or executing code directly. The lack of input validation regarding the expected size of decompressed content is a common oversight in web applications that process external media files without implementing strict quotas or streaming limits for intermediate processing steps.
To mitigate this vulnerability, it is essential to implement robust resource management controls within the image fetching and decomposition logic. Developers should enforce maximum allowable sizes for both compressed payloads and their uncompressed counterparts before they are fully loaded into memory. Utilizing stream-based processing with chunked reading can prevent large files from consuming excessive RAM at once. Additionally, implementing timeout mechanisms and rate limiting on external URL fetches can further reduce the risk of abuse. Upgrading to Open WebUI version 0.11.4 or later is required as these updates include patches that address this specific uncontrolled resource consumption issue by introducing proper bounds checking during image processing operations.