CVE-2023-47106

When a request is sent to Traefik with a URL fragment, Traefik automatically URL encodes and forwards the fragment to the backend server. This violates the RFC because in the origin-form the URL should only contain the absolute path and the query.

When this is combined with another frontend proxy like Nginx, it can be used to bypass frontend proxy URI-based access control
restrictions.

Details

For example, we have this Nginx configuration:

location /admin {
     deny all;
     return 403;
}

This can be bypassed when the attacker is requesting to /#/../admin

This won’t be vulnerable if the backend server follows the RFC and ignores any characters after the fragment.

However, if Nginx is chained with another reverse proxy which automatically URL encode the character # (Traefik) the URL will become

/%23/../admin

And allow the attacker to completely bypass the Access Restriction from the Nginx Front-End proxy.

Here is a diagram to summarize the attack:

PoC

This is the POC docker I've set up. It contains Nginx, Traefik proxies and a backend server running PHP.

https://drive.google.com/file/d/1vLnA0g7N7ZKhLNmHmuJ4JJjV_J2akNMt/view?usp=sharing

This allows the attacker to completely bypass the Access Restriction from Front-End proxy.

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2023-47106 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.10.6, 3.0.0-beta5); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2023-47106? CVE-2023-47106 is a medium-severity improper input validation vulnerability in github.com/traefik/traefik/v2 (go), affecting versions < 2.10.6. It is fixed in 2.10.6, 3.0.0-beta5. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2023-47106? CVE-2023-47106 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2023-47106?
   • github.com/traefik/traefik/v2 (go) (versions < 2.10.6)
   • github.com/traefik/traefik/v3 (go) (versions < 3.0.0-beta5)
4. Is there a fix for CVE-2023-47106? Yes. CVE-2023-47106 is fixed in 2.10.6, 3.0.0-beta5. Upgrade to this version or later.
5. Is CVE-2023-47106 exploitable, and should I be worried? Whether CVE-2023-47106 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-47106 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-47106?
   • Upgrade github.com/traefik/traefik/v2 to 2.10.6 or later
   • Upgrade github.com/traefik/traefik/v3 to 3.0.0-beta5 or later