Vulnerability details

### Summary The forge TLS client's check for a missing server certificate read the wrong property and never ran. A malicious TLS server, or an on-path attacker who removes the server's Certificate message, can make `connection.process()` throw a `TypeError`, which crashes applications that use the forge TLS client. Fixed in node-forge 1.4.1. ### Details After ServerHelloDone, `tls.handleServerHelloDone()` in `lib/tls.js` is meant to reject a server that sent no certificate with a fatal `insufficient_security` alert, after consulting the application's `verify` callback. The check tested `c.serverCertificate`, which is never set (the certificate is stored as `c.session.serverCertificate`), so it never ran. The client state machine allows ServerHelloDone directly after ServerHello, so the handshake continued to `tls.createClientKeyExchange()`, which reads `c.session.serverCertificate.publicKey` and throws a `TypeError` on the null certificate. The exception propagates out of `connection.process()` without calling the `verify` or `error` callbacks. There is no authentication bypass: without a server certificate the client cannot build its RSA key exchange, so the handshake cannot complete. The fix reads `c.session.serverCertificate` and always fails the handshake in that case, still calling `verify` so the application can customize the alert. Failing even when `verify` returns `true` is needed because the key exchange requires the certificate. #### Patches Fixed in node-forge 1.4.1. The TLS client fails the handshake with an `insufficient_security` alert when the server sends no certificate. #### Workarounds Catch exceptions thrown by `connection.process()` in the code that feeds it network data, and close the connection when one occurs. #### Credits Reported by @arpitjain099. ### Proof of concept Connect a forge TLS client (`forge.tls.createConnection({server: false, ...})`) to a server whose first flight contains ServerHello and ServerHelloDone but no Certificate message. For example, run a forge TLS server and remove the Certificate handshake message (type 11) from its first flight before passing it to the client's `process()`. On 1.4.0 the client's `process()` throws "TypeError: Cannot read properties of null (reading 'publicKey')", and the `verify` and `error` callbacks are not called. On 1.4.1 the client calls `verify` with `insufficient_security` and no certificates, calls `error` with "No server certificate provided. Not enough security.", sends a fatal alert and closes the connection. Regression tests are in tests/unit/tls.js ("missing server certificate"). ### Impact Applications that use the forge TLS client (`forge.tls.createConnection` with `server: false`) are affected. A malicious server the application connects to, or an on-path attacker who can modify the unauthenticated handshake, can make the client throw from `connection.process()`. Since `process()` is normally called from a socket data handler, the uncaught exception terminates a Node.js process. There is no confidentiality or integrity impact. Applications using Node.js's own TLS implementation are not affected.