CVE-2026-33898: Local Incus UI web server vulnerable to nuthentication bypass
Summary The web server spawned by incus webui incorrectly validates the authentication token such that an invalid value will be accepted.
Details incus webui runs a local web server on a random localhost port. For authentication, it provides the user with a URL containing an authentication token. When accessed with that token, Incus creates a cookie persisting that token without needing to include it in subsequent HTTP requests.
While the Incus client correctly validates the value of the cookie, it does not correctly validate the token when passed int the URL. This allows for an attacker able to locate and talk to the temporary web server on localhost to have as much access to Incus as the user who ran incus webui.
This can lead to privilege escalation by another local user or an access to the user's Incus instances and possibly system resources by a remote attack able to trick the local user into interacting with the Incus UI web server.
Credit This issue was discovered and reported by the team at 7asecurity
Other sources
Incus is a system container and virtual machine manager. Prior to version 6.23.0, the web server spawned by incus webui incorrectly validates the authentication token such that an invalid value will be accepted. incus webui runs a local web server on a random localhost port. For authentication, it provides the user with a URL containing an authentication token. When accessed with that token, Incus creates a cookie persisting that token without needing to include it in subsequent HTTP requests. While the Incus client correctly validates the value of the cookie, it does not correctly validate the token when passed int the URL. This allows for an attacker able to locate and talk to the temporary web server on localhost to have as much access to Incus as the user who ran incus webui. This can lead to privilege escalation by another local user or an access to the user's Incus instances and possibly system resources by a remote attack able to trick the local user into interacting with the Incus UI web server. Version 6.23.0 patches the issue.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-33898?
CVE-2026-33898 has been classified as a critical vulnerability due to its potential for authentication bypass.
How do I fix CVE-2026-33898?
To mitigate CVE-2026-33898, upgrade to Incus version 6.23.0 or later to ensure proper authentication validation.
What software is affected by CVE-2026-33898?
CVE-2026-33898 affects the Incus web server prior to version 6.23.0 that is spawned by the `incus webui` command.
What is the impact of CVE-2026-33898?
The impact of CVE-2026-33898 allows unauthorized access to the Incus UI web server, potentially compromising system security.
How can I verify if I'm using a vulnerable version for CVE-2026-33898?
You can verify your version of Incus by checking the software properties and confirming if it is below version 6.23.0.