In plain words
Think of this like a security guard who is supposed to check everyone's ID cards before letting them into a building, but sometimes does not actually verify the ID is real. In this case, the security guard is a piece of software called Apache Syncope, and the ID cards are special tokens called JWT¹ that prove a user's identity.
What's broken
The bug is in the Apache Syncope software, specifically in how it checks the cryptographic signature² of these JWT tokens when used with OAuth 2.0³. The versions of Apache Syncope that have this bug are 3.0.0-M0 through 3.0.16, 4.0.0-M0 through 4.0.7, and 4.1.0-M0 through 4.1.2. An attacker can exploit this bug to fake a user's identity if the SRA is configured for OAuth 2.0 without a JWKS⁴ set URI assigned.
How it actually works
Here's how it works: normally, when a user tries to log in, the software checks the JWT token's cryptographic signature to make sure it was really sent by the trusted source. But because of this bug, if the SRA is not set up with a JWKS URI, an attacker can forge a JWT token with a fake signature, and the software will not properly check it, letting the attacker in. This is possible because the software does not correctly verify the signature when the JWKS URI is missing.
Proof of concept
There is a public description of this bug, but it's not clear from the source if there is a fully working proof-of-concept⁵ that demonstrates the bug. A proof-of-concept would show that the flaw is real and can be exploited, making it more urgent to fix. However, the existence of such a proof is not confirmed in the provided information.
Is it real
It's not clear from the source if this bug is being actively exploited in the wild. The bug is considered to be of low severity. One limiting factor is that the SRA needs to be configured for OAuth 2.0 without a JWKS set URI for the bug to be exploitable.
What to do
To fix this bug, users should update their Apache Syncope software to a version that does not have this flaw. This will ensure that the software correctly checks the cryptographic signatures of JWT tokens, preventing attackers from faking user identities.
Terms
- ¹ JWT
- , JSON Web Token, a compact, URL-safe means of representing claims to be transferred between two parties.
- ² cryptographic signature
- , A digital signature is a type of asymmetric cryptography used to verify the authenticity of a message or document.
- ³ OAuth 2.0
- , OAuth 2.0 is an authorization framework that allows a client to access a resource server without sharing the client's credentials.
- ⁴ JWKS
- , JSON Web Key Set, a set of keys containing the public key that can be used to verify the digital signature of a JWT token.
- ⁵ proof-of-concept
- , A proof-of-concept is a demonstration that a bug or vulnerability can be exploited, often used to show the severity of the issue.