RUSTSEC-2026-0285: TLS 1.3 handshake messages incorrectly accepted across encryption level boundaries

What to do

1. See which version you have: cargo tree -i rustls (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p rustls. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example rustls = "0.23.45") or update the dependency that pulls it in.
3. Check again with cargo audit, or paste your Cargo.lock into our Cargo.toml checker.

Details from the advisory

Rustls accepted TLS 1.3 handshake messages sent at the wrong encryption level when they followed a key-changing message in the same record. For example, a plaintext EncryptedExtensions message packed into the same record as the ServerHello was accepted.

RFC 8446 section 5.1 requires that handshake messages do not span key changes, and that implementations terminate the connection with an "unexpected_message" alert if they do.

The handshake transcript is still authenticated, so a network-position attacker cannot use this to alter or complete a handshake; the practical effect is that a peer could send handshake messages that should be encrypted in plaintext without rustls rejecting the connection.

This is functionally the same bug as Go's GO-2026-4340 (CVE-2025-61730).

References

• Package: crates.io/crates/rustls
• Advisory: rustsec.org/advisories/RUSTSEC-2026-0285.html
• Web: github.com/rustls/rustls/pull/3265

From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.

Other advisories for rustls

• Vulnerability HighRUSTSEC-2024-0336 · 2024-04-19`rustls::ConnectionCommon::complete_io` could fall into an infinite loop based on network input
• VulnerabilityRUSTSEC-2024-0399 · 2024-11-22rustls network-reachable panic in `Acceptor::accept`
• Vulnerability MediumRUSTSEC-2026-0346 · 2026-10-14`Debug` impls for client session values expose TLS secrets
• Vulnerability LowRUSTSEC-2026-0347 · 2026-10-14Buffered application data sent to outer server after ECH rejection
• Vulnerability LowRUSTSEC-2026-0348 · 2026-10-14Brotli certificate decompression can allocate up to 1 GiB before authentication
• Vulnerability LowRUSTSEC-2026-0349 · 2026-10-14Unauthenticated ServerHello can downgrade later connections to classical key exchange

Full security history of rustls