LocalStack: Remote code execution via cross-site scripting in CloudFormation deploy UI
Summary
LocalStack 4.9.2 contains a flaw in its CloudFormation deployment page (/_localstack/cloudformation/deploy). A crafted template URL passed as templateURL can cause attacker-controlled script to run in the victim's browser, and the script can then use LocalStack's Lambda feature to execute code inside the LocalStack Docker container. The attack requires a victim to open a crafted link while LocalStack is running, and the API origin accepts unauthenticated requests. NVD scores the issue 9.6 (Critical), but a CISA vulnrichment issue disputes this and proposes 5.4 for a reflected XSS.
Affected
- LocalStack 4.9.2 (per NVD description)
- Wider range of 4.0.0 to 4.10.0 reported by Vulners; not verified
- Unknown whether other versions are affected
Fixed in
Unknown. The referenced fix is PR 13293, which removes the deprecated deploy GUI tool. No release containing this fix has been confirmed.
Workaround
- Do not expose LocalStack to untrusted networks; bind its port to localhost only
- Block or remove the /_localstack/cloudformation/deploy path at a reverse proxy (unsourced recommendation)
- Do not open untrusted links in a browser on a machine running LocalStack
Exploitation
- No confirmed exploitation in the wild; CISA KEV: No
- A public write-up with a proof of concept exists (cyberroute.github.io)
- CISA SSVC: Exploitation poc, Automatable no, Technical Impact total
- VulDB states technical details are known but no exploit is available
Our recommendation
- Identify all LocalStack instances on developer laptops and CI runners
- Remove LocalStack from any network reachable by users or the internet
- Block the deploy path at a reverse proxy if the tool must remain running
- Update to a release that includes PR 13293 once its release number is confirmed
- Monitor the NVD and the LocalStack release notes for the final score and fixed version
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- CVE-2025-65200 on CVEMon cvemon.intruder.io
- CISA vulnrichment issue 343 github.com
- Write-up with PoC (cyberroute) cyberroute.github.io
- LocalStack PR 13293 github.com
- Vulnerable deploy_ui.py at referenced commit github.com
- VulDB entry 425363 vuldb.com
- Vulners MEND:CVE-2025-65200 vulners.com
- Strix CVE page www.strix.ai
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 30 Oct 2026, 22:17.
Original description (NVD)
An issue was discovered in localstack 4.9.2 allowing attackers to execute arbitrary code via crafted content hosted on a web-accessable URL and when passed said URL in the the templateURL to the _localstack/cloudformation/deploy endpoint, the hosted content can get executed in the context of the docker container.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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