Man-in-the-Middle (MitM) Affecting async-nats package, versions <0.29.0


Severity

Recommended
0.0
medium
0
10

CVSS assessment made by Snyk's Security Team. Learn more

Threat Intelligence

Exploit Maturity
Proof of concept

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  • Snyk IDSNYK-RUST-ASYNCNATS-3373060
  • published26 Mar 2023
  • disclosed24 Mar 2023
  • creditUnknown

Introduced: 24 Mar 2023

CVE NOT AVAILABLE CWE-300  (opens in a new tab)

How to fix?

Upgrade async-nats to version 0.29.0 or higher.

Overview

async-nats is an async Rust NATS client.

Affected versions of this package are vulnerable to Man-in-the-Middle (MitM) due to TLS certificate common name validation bypass. The common name of the server's TLS certificate is validated against the hostname provided by the server's plaintext INFO message during the initial connection setup phase. A MitM proxy can tamper with the host field's value by substituting it with the common name of a valid certificate it controls, fooling the client into accepting it.

PoC

  1. The NATS Rust client tries to establish a new connection
  2. The connection is intercepted by a MitM proxy
  3. The proxy makes a separate connection to the NATS server
  4. The NATS server replies with an INFO message
  5. The proxy reads the INFO, alters the host JSON field and passes the tampered INFO back to the client
  6. The proxy upgrades the client connection to TLS, presenting a certificate issued by a certificate authority present in the client's keychain. In the previous step the host was set to the common name of said certificate
  7. rustls accepts the certificate, having verified that the common name matches the attacker-controlled value it was given
  8. The client has been fooled by the MitM proxy into accepting the attacker-controlled certificate

CVSS Scores

version 3.1