Required mTLS route admits a resumed session whose client cert has since expired

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Evaluación

Dificultad
3/5
Tiempo estimado
1-2 días
Aptitud para principiantes
35/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Activo
Stack tecnológico
rust
Área
networking, security

Línea de trabajo

Start at the handling of HandshakeKind::Resumed in symphony's TLS accept path, and read how the PROXY v2 re-verification already re-checks a resumed chain at the current time. The rustls resumption code in src/server/tls13.rs and src/server/tls12.rs (rustls 0.23.45) explains why the client verifier is skipped. Done means that on routes with mtls.requireClientCert: true, a resumed connection whose restored chain fails verification against the route's CA roots is closed, with a test for an expired cert resumed on a non-PROXY route.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

Summary

On a route with mtls.requireClientCert: true, a client whose certificate expires after its TLS session was issued can keep connecting by resuming that session. The handshake's certificate check does not run on resumption.

Mechanism

  • Resumption skips the verifier. rustls restores the client chain stored with the session and never calls ClientCertVerifier::verify_client_cert again (rustls 0.23.45 src/server/tls13.rs ~line 374, src/server/tls12.rs ~line 289).
  • Window. The session lasts as long as the ticket (rustls ring Ticketer, about 6h) for TLS 1.3. For TLS 1.2 it also lasts while the session stays in the per-config session cache (ServerSessionMemoryCache, 1024 entries). After that the client must do a full handshake, and the expired cert is rejected.
  • A policy change never resumes across. Each route's ServerConfig owns its ticketer and session store. The TLS config cache key includes the CA bundle bytes and requireClientCert, so changing either builds a new config whose tickets the old sessions can't use.
  • PROXY v2 routes are already covered for authorization. On sourceAddressHeader: 'proxyProtocolV2', symphony re-verifies a resumed chain at the current time before reporting it. An expired chain is reported as presented but unverified (verify=1, no 0xE2 chain TLVs), so Harper's PROXY reader treats the client as unauthorized.
  • Exposed case: required routes with no PROXY v2. No identity reaches the upstream, and symphony's rejection was the only enforcement. Those routes admit the resumed connection.

This is the same default behaviour as OpenSSL and nginx. Symphony has no revocation (CRL/OCSP) support, so expiry is the only thing this window can miss.

Proposed fix

After a resumed handshake (HandshakeKind::Resumed) on a required route, re-verify the restored chain against the route's CA roots at the current time, on every route whatever its sourceAddressHeader. Close the connection if verification fails. This costs one chain verification per resumed connection on required routes. Full handshakes are unchanged, since rustls already verified them.

Related

  • HarperFast/symphony#62 and HarperFast/symphony#63 (the PR closing them adds the PROXY v2 re-verification described above)

🤖 Generated by Claude Opus 5.5 via Claude Code; posted via @kriszyp.

Review-Deferral: 71a692d3fc7de781 severity=minor category=security

Lenguaje dominante
Rust
Estrellas
1
Forks
0
Merge medio
19 h 12 min
PR fusionados (30 d)
13

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