CVE-2023-33189 - Exploiting Authorization Bypass in Pomerium (with Exploit Details and Patch Guidance)
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Introduction
In 2023, a critical vulnerability—CVE-2023-33189—was found in Pomerium, a popular identity and context-aware access proxy. This flaw could let attackers bypass normal access controls with specially crafted requests, leading to unauthorized access to protected resources. If you’re using Pomerium and haven’t updated after June 2023, you *need* to read this.
This long read will break down the vulnerability, demonstrate how it works with code snippets, and point you toward the official fixes and resources.
Background: What is Pomerium?
Pomerium acts as a proxy that controls who can access internal applications based on identity (like SSO), context, and specific rules. It sits in front of your web apps and lets you enforce granular policies—a great tool for Zero Trust architectures.
See the project site for more background.
The Vulnerability in Simple Terms
The vulnerability is about Pomerium making wrong authorization decisions when handling *specially crafted requests*. An attacker could structure their web requests in certain ways to trick Pomerium into giving access even if the policy denies it.
How Does It Work?
Pomerium’s role is to check incoming requests and match them against access rules. Due to unsafe parsing of certain requests (especially path or header handling), logic bugs allowed attackers to manipulate the request and bypass the policy checks.
Send a request that should be blocked, but is (due to the bug) allowed through by Pomerium.
This is similar to classic HTTP split path or ambiguous request parsing bugs.
Let’s say you have Pomerium enforcing this policy
# example policy: only alice@example.com can access /admin
routes:
- from: https://your-app.company.com
to: http://localhost:808
policy:
- allow:
email:
- alice@example.com
path: /admin
Suppose /admin should be restricted. Pomerium checks requests for /admin and denies everyone except Alice.
Potential Exploit: Using double URL encoding or path confusion, the attacker sends
GET /%61dmin HTTP/1.1
Host: your-app.company.com
or using ambiguous headers
GET /admin HTTP/1.1
Host: your-app.company.com
X-Original-URL: /public
*In some vulnerable versions, Pomerium could treat these requests as allowed, depending on how the rule engine parses them.*
Why? Because Pomerium checks *one interpretation* of the path, but the underlying application or policy may interpret it differently.
Original References and Confirmations
- GitHub Security Advisory for CVE-2023-33189
- NVD entry on CVE-2023-33189
- Pomerium release notes
A typical attacker’s flow
1. Recon: Learn which paths are protected by Pomerium’s policy (e.g., /admin).
Craft Request: Use URL encoding, double slashes, or confusing headers to mask the true path.
3. Send Request: The request reaches Pomerium. The faulty logic interprets the crafted request as *unprotected* or as matching a different policy.
4. Unauthorized Access: Pomerium allows access, letting the attacker interact with the protected resource.
*Note:* The exact exploit depends on the specific version and policy configuration, as well as how underlying applications route requests.
Mitigation and Patch Instructions
If you control a Pomerium deployment, update immediately. Versions with corresponding security fixes are:
Anything older is vulnerable!
Upgrading is the only way to fully close the hole.
Find official instructions here: Pomerium documentation.
Example for Docker
docker pull pomerium/pomerium:latest
Conclusion
CVE-2023-33189 is a classic example of how complicated modern web access control is—and how small bugs can lead to big breaches. If you use Pomerium, make sure you’re running a patched version.
Want more official info? Check here
Timeline
Published on: 05/30/2023 06:16:00 UTC
Last modified on: 06/05/2023 17:04:00 UTC