CVE-2026-109298 in Open WebUI
Summary
by MITRE • 10/12/2026
Open WebUI 0.11.0 before 0.11.4 compiles user-chosen grep patterns for its knowledge and chat file search tools with a regex engine that expands nested counted repetition unbounded at compile time and caches the result. Authenticated users can have the model call grep_knowledge_files with short nested-repetition patterns, blocking the event loop and exhausting worker memory.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability identified in Open WebUI versions prior to 0.11.4 represents a critical server-side resource exhaustion flaw rooted in improper handling of regular expression compilation within its search functionality. The core technical issue lies in how the application processes user-supplied input for knowledge and chat file searches using grep patterns that are compiled into regex engines capable of expanding nested counted repetitions without bounds at compile time. This specific behavior allows an authenticated attacker to craft maliciously structured pattern strings containing deeply nested quantifiers, such as repeated groups with variable length constraints like (a+){100}. When the application attempts to compile these patterns for use in file search operations, the regex engine enters a state of catastrophic backtracking or excessive memory allocation during the compilation phase rather than at runtime execution. This process is not protected by sufficient timeouts or resource limits, causing the operation to consume disproportionate amounts of CPU and memory resources on the server side.
From an operational perspective, this flaw directly impacts the availability of the Open WebUI service through a denial-of-service mechanism. Because the regex compilation occurs within the main event loop or blocks worker threads responsible for handling user requests, the successful exploitation effectively freezes the application's ability to process legitimate traffic. The caching of these compiled patterns exacerbates the issue by potentially storing large amounts of memory in an unbounded manner across multiple sessions or search queries. An authenticated attacker can repeatedly trigger this condition with short but complex nested-repetition patterns, leading to a rapid exhaustion of worker memory and eventual crash or severe degradation of service performance for all users connected to the instance. This is particularly dangerous because it requires only authentication, which may be easily obtained through credential stuffing or other common attack vectors, lowering the barrier for exploitation significantly compared to unauthenticated remote code execution flaws.
This vulnerability aligns with CWE-400 Uncontrolled Resource Consumption and specifically relates to CWE-1325 Incorrect Regular Expression Logic where patterns are not validated against complexity limits before compilation. In terms of adversary tactics, this behavior maps to MITRE ATT&CK technique T1499 Endpoint Denial of Service, as the attacker aims to disrupt service availability rather than compromise data integrity or confidentiality directly. The exploitation relies on the application's trust in user-supplied input for search queries without implementing strict length limits, complexity checks, or sandboxing mechanisms for regex compilation. To mitigate this risk, immediate updates to Open WebUI version 0.11.4 or later are required as they address these specific regex handling issues. In environments where upgrading is not immediately feasible, administrators should implement network-level rate limiting on search endpoints and consider deploying a web application firewall with rules that detect and block regular expressions containing deeply nested quantifiers or excessive repetition patterns before they reach the application logic.