CVE-2026-15685 in Ollama
Summary
by MITRE • 07/14/2026
Ollama downloadBlob Improper Validation of Array Index Denial-of-Service Vulnerability. This vulnerability allows remote attackers to create a denial-of-service condition on affected installations of Ollama. Authentication is not required to exploit this vulnerability.
The specific flaw exists within the downloadBlob function. The issue results from the lack of proper validation of user-supplied data, which can result in a memory access past the end of an allocated array. An attacker can leverage this vulnerability to create a denial-of-service condition on the system. Was ZDI-CAN-27277.
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Analysis
by VulDB Data Team • 07/14/2026
The Ollama downloadBlob function contains a critical improper validation of array index vulnerability that enables remote attackers to execute denial-of-service attacks without requiring authentication. This flaw represents a classic buffer over-read condition where insufficient input validation allows malicious data to access memory locations beyond the bounds of allocated arrays. The vulnerability specifically impacts the downloadBlob functionality within Ollama's codebase, making it particularly dangerous as it affects core file handling operations that are essential for the application's normal functioning.
The technical implementation of this vulnerability stems from inadequate boundary checking within the array indexing logic used by the downloadBlob function. When processing user-supplied data during blob downloads, the system fails to validate array indices before accessing memory locations, creating opportunities for attackers to supply malicious inputs that cause memory access violations. This type of flaw aligns with CWE-129, which addresses improper validation of array index values, and represents a fundamental failure in input sanitization protocols. The vulnerability operates at the application level where user-controllable data flows directly into memory access operations without proper bounds checking mechanisms.
The operational impact of this vulnerability extends beyond simple service disruption as it can effectively render affected Ollama installations unusable through controlled resource exhaustion or memory corruption. Attackers can exploit this weakness by crafting specific blob download requests that trigger the array over-read condition, potentially causing application crashes, system instability, or complete service unavailability. This denial-of-service scenario affects not only individual user experiences but also broader deployment environments where Ollama services may be critical infrastructure components. The vulnerability's remote exploitability means that attackers can target systems from external networks without requiring local access or authentication credentials, making it particularly dangerous in production environments.
Mitigation strategies for this vulnerability should focus on implementing robust input validation mechanisms within the downloadBlob function and other related array handling operations. Security measures must include bounds checking for all array indices before memory access, proper input sanitization of user-supplied data, and comprehensive error handling that prevents memory access violations from causing system instability. Organizations should also consider implementing network-level protections such as rate limiting and access controls to reduce the effectiveness of potential exploitation attempts. The vulnerability's classification under ATT&CK technique T1499.004 for network denial-of-service indicates that defensive measures should include monitoring for unusual download patterns and implementing intrusion detection systems that can identify malicious blob request sequences. Regular security updates and patch management processes are essential to address this issue promptly, as the flaw exists in the core data processing functionality of the application.
The broader implications of this vulnerability highlight the critical importance of input validation in preventing memory corruption attacks within modern software applications. This flaw demonstrates how seemingly simple array access operations can become significant security risks when proper validation controls are absent from the codebase. Organizations relying on Ollama or similar applications should conduct comprehensive security assessments to identify similar vulnerabilities in their software stacks and implement defensive programming practices that align with industry best practices for preventing buffer over-read conditions and related memory safety issues.