Ollama downloadBlob Array Index Validation DoS

Executive Summary

CVE-2026-15685 is a denial-of-service vulnerability in Ollama's software. It exists in the downloadBlob function, where improper validation of user-supplied data allows an attacker to access memory beyond the end of an allocated array.

This flaw does not require authentication, meaning any remote attacker can exploit it. The vulnerability can cause the system to crash or become unresponsive, leading to a denial-of-service condition.

• The issue is classified as an improper validation of array index vulnerability.
• The CVSS v3.0 base score is 7.5, indicating high severity with no impact on confidentiality or integrity but a high impact on availability.

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Detection Guidance

Detecting this vulnerability on your network or system requires checking for signs of exploitation or verifying if the affected Ollama software version is running. Since the vulnerability is in the downloadBlob function and can be exploited remotely without authentication, you can monitor network traffic for unusual patterns targeting Ollama services.

• Check if Ollama is running on your system. On Linux, you can use: ps aux | grep ollama
• Inspect network traffic for unexpected connections to Ollama services. Use tools like tcpdump or Wireshark to filter traffic on the default Ollama ports (if known). Example: tcpdump -i any port <Ollama_port>
• Review system logs for crashes or unusual behavior in Ollama processes. Check logs in /var/log/ or journalctl -u ollama (if running as a service).
• Verify the installed version of Ollama. If the version is outdated or unpatched, it may be vulnerable. Use: ollama --version or check package managers like apt list --installed | grep ollama (Debian-based) or rpm -qa | grep ollama (RHEL-based).

Since the vulnerability involves improper array index validation, exploitation may lead to process crashes. Monitoring for frequent crashes or unresponsive Ollama services can indicate an attack.

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Impact Analysis

If you use Ollama, this vulnerability could allow an attacker to remotely crash or disrupt your system without needing any credentials.

• The denial-of-service condition could lead to downtime, affecting services or applications relying on Ollama.
• Since no authentication is required, the attack surface is broad, increasing the risk of exploitation.

The impact is primarily on system availability, meaning your software or services may become unavailable until the issue is resolved.

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Compliance Impact

This vulnerability may indirectly affect compliance with standards and regulations depending on how Ollama is used in your environment.

• GDPR: If Ollama processes personal data and the denial-of-service disrupts data processing or availability, it could violate GDPR's requirements for data availability and resilience (Article 32).
• HIPAA: If Ollama is used in a healthcare setting to handle protected health information (PHI) and the vulnerability causes downtime, it may violate HIPAA's availability requirements for electronic PHI.

While the vulnerability itself does not directly expose data, the resulting denial-of-service could lead to non-compliance if it disrupts critical services or data access.

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Mitigation Strategies

The following steps can help mitigate the risk posed by CVE-2026-15685:

• Restrict interaction with the Ollama product. Limit access to the service to trusted networks or users only. Use firewalls or network segmentation to block unauthorized access.
• Update Ollama to the latest version if a patch is available. Check the official Ollama repository or vendor advisories for updates.
• Disable the Ollama service if it is not critical to your operations until a patch is applied.
• Monitor the system for signs of exploitation, such as unexpected crashes or high resource usage in Ollama processes.
• Apply network-level protections, such as intrusion detection/prevention systems (IDS/IPS), to detect and block exploitation attempts.

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