CVE-2025-66959: Ollama Input Validation flaw enables

CISO Take

CVE-2025-66959 is a network-exploitable DoS in Ollama's GGUF decoder requiring zero authentication — any Ollama instance exposed to untrusted networks is at immediate risk of being crashed. Patch to a version past 0.12.10 immediately and restrict Ollama's API port (default 11434) to localhost or trusted network segments only. If you cannot patch today, a firewall rule blocking external access to port 11434 is an effective temporary control.

What is the risk?

HIGH. The CVSS 7.5 score understates operational risk for AI teams: GGUF is the dominant model format for self-hosted LLM inference, and Ollama is the de facto local LLM runtime for thousands of enterprise deployments. AC:Low + PR:None + UI:None means exploitation is trivial and automatable. The attack surface is wide — Ollama instances are routinely misconfigured to bind on 0.0.0.0 rather than localhost, making them reachable without any credential. The DoS impact translates directly to loss of AI-assisted workflows, internal copilot tools, and any production service proxying through Ollama.

What systems are affected?

Package	Ecosystem	Vulnerable Range	Patched
Ollama	pip	—	No patch
174.6K 1.6K dependents Pushed 3d ago 12% patched ~0d to patch Full package profile →

Do you use Ollama? You're affected.

How severe is it?

CVSS 3.1

7.5 / 10

EPSS

4.5%

chance of exploitation in 30 days

Higher than 90% of all CVEs

Source: EPSS v3 — FIRST.org

Exploitation Status

Exploit Available

Exploitation: MEDIUM

Sophistication

Trivial

Exploitation Confidence

medium

○ CISA SSVC: Public PoC

○ Public PoC indexed (trickest/cve)

Composite signal derived from CISA KEV, VulnCheck KEV, CISA SSVC, EPSS, Metasploit, Exploit-DB, trickest/cve, Nuclei templates, and inthewild.io exploitation reports.

What is the attack surface?

AV Network

AC Low

PR None

UI None

S Unchanged

C None

I None

A High

What should I do?

5 steps

PATCH

Upgrade Ollama beyond version 0.12.10. Monitor https://github.com/ollama/ollama/releases for a fixed release.
NETWORK ISOLATION (immediate workaround): Ensure Ollama binds to 127.0.0.1 only (default is localhost, verify with ss -tlnp | grep 11434). Block port 11434 at the host firewall and any network perimeter for all non-whitelisted sources.
REVERSE PROXY WITH AUTH

If Ollama must be network-accessible, front it with nginx/Caddy requiring authentication — Ollama itself has no native auth.
DETECTION

Monitor for Ollama process crashes/restarts, unusual HTTP 5xx spikes on port 11434, and oversized or malformed POST payloads to /api endpoints. Alert on process exits from the Ollama service unit.
INVENTORY

Identify all Ollama instances in your environment — dev workstations with open Wi-Fi connections are a common overlooked exposure.

What does CISA's SSVC say?

Decision Track*

Exploitation poc

Automatable Yes

Technical Impact partial

Source: CISA Vulnrichment (SSVC v2.0). Decision based on the CISA Coordinator decision tree.

How is it classified?

DoS Inference Framework AML.T0029 - Denial of AI Service AML.T0034 - Cost Harvesting AML.T0049 - Exploit Public-Facing Application

Which compliance frameworks are affected?

This CVE is relevant to:

EU AI Act

Article 15 - Accuracy, robustness and cybersecurity

ISO 42001

A.6.2.6 - AI system availability and resilience

NIST AI RMF

MANAGE 2.2 - Mechanisms to sustain deployed AI system value and manage risks MANAGE 2.4 - Residual risks are managed and monitored

OWASP LLM Top 10

LLM04 - Model Denial of Service

Frequently Asked Questions

What is CVE-2025-66959?

CVE-2025-66959 is a network-exploitable DoS in Ollama's GGUF decoder requiring zero authentication — any Ollama instance exposed to untrusted networks is at immediate risk of being crashed. Patch to a version past 0.12.10 immediately and restrict Ollama's API port (default 11434) to localhost or trusted network segments only. If you cannot patch today, a firewall rule blocking external access to port 11434 is an effective temporary control.

Is CVE-2025-66959 actively exploited?

Proof-of-concept exploit code is publicly available for CVE-2025-66959, increasing the risk of exploitation.

How to fix CVE-2025-66959?

1. PATCH: Upgrade Ollama beyond version 0.12.10. Monitor https://github.com/ollama/ollama/releases for a fixed release. 2. NETWORK ISOLATION (immediate workaround): Ensure Ollama binds to 127.0.0.1 only (default is localhost, verify with `ss -tlnp | grep 11434`). Block port 11434 at the host firewall and any network perimeter for all non-whitelisted sources. 3. REVERSE PROXY WITH AUTH: If Ollama must be network-accessible, front it with nginx/Caddy requiring authentication — Ollama itself has no native auth. 4. DETECTION: Monitor for Ollama process crashes/restarts, unusual HTTP 5xx spikes on port 11434, and oversized or malformed POST payloads to /api endpoints. Alert on process exits from the Ollama service unit. 5. INVENTORY: Identify all Ollama instances in your environment — dev workstations with open Wi-Fi connections are a common overlooked exposure.

What systems are affected by CVE-2025-66959?

This vulnerability affects the following AI/ML architecture patterns: model serving, local LLM inference, RAG pipelines, AI development environments, internal AI copilot infrastructure.

What is the CVSS score for CVE-2025-66959?

CVE-2025-66959 has a CVSS v3.1 base score of 7.5 (HIGH). The EPSS exploitation probability is 4.55%.

What is the AI security impact?

Affected AI Architectures

model servinglocal LLM inferenceRAG pipelinesAI development environmentsinternal AI copilot infrastructure

MITRE ATLAS Techniques

AML.T0029 Denial of AI Service

AML.T0034 Cost Harvesting

AML.T0049 Exploit Public-Facing Application

Compliance Controls Affected

EU AI Act: Article 15

ISO 42001: A.6.2.6

NIST AI RMF: MANAGE 2.2, MANAGE 2.4

OWASP LLM Top 10: LLM04

What are the technical details?

Original Advisory

An issue in ollama v.0.12.10 allows a remote attacker to cause a denial of service via the GGUF decoder

Exploitation Scenario

An adversary scans corporate IP ranges or cloud VPC subnets for open port 11434 (Ollama default). Upon finding a responsive instance, they craft a GGUF file with a maliciously oversized or invalid length field in the decoder metadata — as documented in the PoC blog referenced in the CVE. They POST this payload to Ollama's model load or generate endpoint. The GGUF decoder attempts to copy a buffer of the attacker-controlled length without bounds checking, triggering a panic that crashes the Ollama process. If Ollama lacks a process supervisor (systemd with Restart=always), the service stays down. In environments where AI copilots, RAG systems, or model-serving APIs depend on this Ollama instance, the downstream services become unavailable — causing a cascading outage without requiring any credentials or prior access.

Weaknesses (CWE)

CWE-20 Improper Input Validation CWE-400 Uncontrolled Resource Consumption

CWE-20 — Improper Input Validation: The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

[Architecture and Design] Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build "recognizers" for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses. [REF-1109] [REF-1110] [REF-1111]
[Architecture and Design] Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).

Source: MITRE CWE corpus.