External risk intelligence

LocalStack Code Execution via CloudFormation Deploy Template URL

CVE advisorySeverity: CRITICAL (CVSS 9.6)

CVE-2025-65200

LocalStack is designed as a local development and testing tool that emulates cloud environments. While the affected endpoint is network-accessible, standard deployment patterns involve running LocalStack within isolated developer environments, CI/CD pipelines, or internal networks, rather than exposing it directly to the public internet.

Cross-site Scripting

Halo Surface Signal: 2 out of 5 — less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

An issue has been identified in LocalStack, a tool used for developing and testing cloud applications, that could allow an attacker to execute arbitrary code. This vulnerability arises when a specially crafted URL is provided to a specific endpoint, enabling the execution of content within the containerized environment. The main concern is confirming the relevance and potential exposure of this vulnerability to our systems.

Code execution via crafted web content.
Confirms relevance and exposure to our systems.
Assess risk and confirm impact on systems.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by tricking a user into visiting a specially crafted URL. This URL would point to malicious content hosted on a web-accessible server. When this URL is provided to a specific LocalStack endpoint, the hosted content is executed within the Docker container where LocalStack is running, potentially allowing the attacker to achieve code execution.

No authentication needed for entry.
Triggered by user visiting a crafted URL.
Risk of arbitrary code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an unauthenticated attacker to execute arbitrary code within the context of a Docker container running LocalStack. This may occur when a user is tricked into accessing a specially crafted URL, which then directs LocalStack to deploy a malicious template hosted on a web-accessible URL. The malicious content could then be executed within the container.

Arbitrary code execution in container.
User visits malicious template URL.
Compromised development or testing environment.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability primarily affects teams responsible for managing development and testing environments, such as platform or DevOps teams. The initial step should be to identify all instances of the affected technology, determine their exposure and criticality, locate the accountable owner for each instance, and then prioritize remediation efforts based on risk.

Platform and DevOps teams own the issue.
Verify instance reachability and criticality.
Plan remediation based on identified risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is LocalStack?

LocalStack is a software tool that emulates cloud service environments locally. Developers and DevOps engineers use it to build, test, and debug cloud-native applications on their own machines or within isolated CI/CD pipelines without needing a live connection to a public cloud provider.

What does CWE-79 mean in the context of CVE-2025-65200?

CWE-79 refers to Improper Neutralization of Input During Web Page Generation, commonly known as Cross-Site Scripting (XSS). In this vulnerability, the system fails to safely handle input provided via a URL, allowing malicious content to be treated as legitimate instructions and executed unexpectedly within the environment.

How is this LocalStack vulnerability triggered?

The flaw is triggered when a user provides a crafted web-accessible URL to the specific cloudformation/deploy endpoint. If the URL points to malicious content, that content can be executed inside the Docker container. Simply having LocalStack running does not trigger the bug; it requires the processing of an externally provided, malicious template URL.

Do I need to worry about CVE-2025-65200 if my LocalStack is internal?

While LocalStack is often run in isolated developer or internal environments, Halo Surface Signal notes that the affected endpoint is network-accessible. If your instance is reachable from untrusted networks or if users within your organization can be tricked into interacting with malicious external links, you should consider the risk of unauthorized execution.

How should I respond to this LocalStack threat?

Begin by identifying all running instances of LocalStack within your organization to understand where this software is deployed. Once identified, evaluate the accessibility of these instances and prioritize those that are most exposed. Consult the project maintainers for available updates and implement access controls to limit interaction with the affected deployment endpoint.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.