CVE-2025-15514: Ollama Null Pointer Dereference DoS Flaw

CVE-2025-15514 Overview

CVE-2025-15514 is a null pointer dereference vulnerability affecting Ollama versions 0.11.5-rc0 through 0.13.5. The flaw exists in the multi-modal model image processing functionality, specifically in how the application handles base64-encoded image data via the /api/chat endpoint. When processing malformed image data, the application fails to validate that decoded data represents valid media before passing it to internal processing functions, leading to a denial of service condition.

Critical Impact

Remote attackers can crash the Ollama runner process by sending specially crafted base64 image data, causing complete service unavailability for all users until manual restart.

Affected Products

• Ollama versions 0.11.5-rc0 through 0.13.5
• Multi-modal model deployments using the /api/chat endpoint
• Systems accepting user-supplied image data for AI model processing

Discovery Timeline

• 2026-01-12 - CVE-2025-15514 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-15514

Vulnerability Analysis

This vulnerability is classified as CWE-395 (Use of NullPointerException Catch to Detect NULL Pointer Dereference), manifesting as a null pointer dereference in Ollama's multi-modal image processing pipeline. The vulnerability allows unauthenticated remote attackers to trigger a denial of service condition through the network-accessible /api/chat endpoint.

The flaw occurs during the processing of base64-encoded image data. When the mtmd_helper_bitmap_init_from_buf function receives malformed input, it returns NULL to indicate failure. However, the calling code does not verify this return value before attempting to dereference the pointer in subsequent operations. This oversight causes a segmentation fault when the NULL pointer is accessed, immediately crashing the runner process.

Root Cause

The root cause is insufficient error handling in the image processing code path. The mtmd_helper_bitmap_init_from_buf function is designed to return NULL when it cannot initialize a valid bitmap from the provided buffer data. The vulnerability exists because the code assumes this function will always succeed, proceeding to dereference the returned pointer without first checking if it is NULL. This violates defensive programming principles where all external function return values should be validated before use.

Attack Vector

The attack is exploitable remotely over the network without authentication. An attacker sends a POST request to the /api/chat endpoint containing base64-encoded data that appears to be an image but decodes to invalid media content. When Ollama attempts to process this data through its multi-modal pipeline, the image initialization function fails and returns NULL. The subsequent null pointer dereference triggers a segmentation fault, crashing the runner process and rendering the AI model unavailable to all users.

The attack mechanism involves crafting base64 strings that:

1. Pass initial base64 decoding validation
2. Fail image format validation in mtmd_helper_bitmap_init_from_buf
3. Cause NULL to be returned without proper error handling

For detailed technical analysis, see the VulnCheck Security Advisory and the Huntr Bounty Report.

Detection Methods for CVE-2025-15514

Indicators of Compromise

• Unexpected crashes or restarts of the Ollama runner process
• Segmentation fault (SIGSEGV) errors in system logs associated with Ollama
• Increased volume of requests to /api/chat with image data from untrusted sources
• Service unavailability patterns correlated with incoming API requests containing base64 image payloads

Detection Strategies

• Monitor Ollama process health and implement alerting for unexpected process terminations
• Analyze network traffic for anomalous patterns in /api/chat requests, particularly those with unusual base64-encoded image data
• Implement request logging to capture and review image upload attempts that precede service crashes
• Deploy application-level monitoring to detect null pointer dereference exceptions before they cause crashes

Monitoring Recommendations

• Enable detailed logging for the Ollama /api/chat endpoint to track all incoming requests with image data
• Configure process monitoring to alert on Ollama runner crashes with automatic correlation to recent API activity
• Implement rate limiting and input validation at the network perimeter for requests containing base64 image payloads
• Deploy SentinelOne Singularity Platform to detect crash patterns and anomalous process behavior indicative of exploitation attempts

How to Mitigate CVE-2025-15514

Immediate Actions Required

• Restrict access to the /api/chat endpoint to trusted networks and authenticated users only
• Implement input validation at the application gateway to reject malformed base64 image data before it reaches Ollama
• Enable process monitoring with automatic restart capabilities to minimize service disruption
• Review network access controls to limit exposure of Ollama endpoints to untrusted sources

Patch Information

At the time of publication, users should monitor the official Ollama repository and Ollama website for security updates addressing this vulnerability. Upgrade to the latest patched version as soon as it becomes available. Review the VulnCheck Security Advisory for vendor response updates.

Workarounds

• Deploy a reverse proxy or API gateway in front of Ollama that validates image data before forwarding requests
• Disable multi-modal image processing functionality if not required for your deployment
• Implement network segmentation to isolate Ollama instances from untrusted network segments
• Use firewall rules to restrict /api/chat access to known, trusted IP addresses only

# Example: Restrict Ollama API access using iptables
# Allow only trusted network to access Ollama API port
iptables -A INPUT -p tcp --dport 11434 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 11434 -j DROP