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9.1
CVE-2026-89422: Erlang OTP TLS 1.3 client can trust fake server
CVE-2026-89422 · published 1 day ago
Summary
The TLS 1.3 client code in Erlang/OTP (including Debian and Canonical packages) can be fooled by a server that adds an unexpected pre‑shared key tag. This causes the client to skip all certificate checks, letting an attacker impersonate the intended server. Upgrade to the latest Erlang/OTP release or apply the vendor’s patch to restore proper server authentication.
What to do
- Update erlang otp to version 29.1.1.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| – | erlang | otp |
< * Fix: upgrade to 29.1.1
|
| Debian:12 | debian | erlang | All versions |
| Ubuntu:Pro:14.04:LTS | canonical | erlang | All versions |
Original advisory text
TLS 1.3 client skips server authentication when ServerHello carries an unsolicited pre_shared_key extension
## Summary
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.
## Impact
An attacker that answers a TLS 1.3 client connection, either as the host the client dials or as an on-path attacker, completes the handshake as the intended server and holds all traffic keys. It can read everything the application sends, including credentials, tokens and request bodies, and forge every response. Any consumer of `ssl:connect` that negotiates TLS 1.3 is affected, including `httpc` over HTTPS, database and messaging client libraries, and TLS distribution clients.
## Workarounds
Restrict affected clients to TLS 1.2 by setting `{versions, ['tlsv1.2']}` in the client's `ssl` options. This avoids the vulnerable code path at the cost of losing TLS 1.3.
No configuration both keeps TLS 1.3 and mitigates the issue.
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.
## Impact
An attacker that answers a TLS 1.3 client connection, either as the host the client dials or as an on-path attacker, completes the handshake as the intended server and holds all traffic keys. It can read everything the application sends, including credentials, tokens and request bodies, and forge every response. Any consumer of `ssl:connect` that negotiates TLS 1.3 is affected, including `httpc` over HTTPS, database and messaging client libraries, and TLS distribution clients.
## Workarounds
Restrict affected clients to TLS 1.2 by setting `{versions, ['tlsv1.2']}` in the client's `ssl` options. This avoids the vulnerable code path at the cost of losing TLS 1.3.
No configuration both keeps TLS 1.3 and mitigates the issue.
References
- https://cna.erlef.org/cves/CVE-2026-89422.html URL
- https://github.com/erlang/otp/commit/21b8a1b0ad0adf200682b3854bc50114ab2b8c62 URL
- https://github.com/erlang/otp/commit/98c66c858113949c4262d26cd7d426c4b09d2b35 Patch
- https://github.com/erlang/otp/commit/afec5156361bb50d3607c7c1a453c19b9149b324 Patch
- https://github.com/erlang/otp/commit/fd1d9d07fc92ec0d59f96dfb66182195882bb7dd Patch
- https://github.com/erlang/otp/security/advisories/GHSA-rgxr-4g4w-j875 Vendor Advisory
- https://osv.dev/vulnerability/EEF-CVE-2026-89422 Third Party Advisory
- https://www.erlang.org/doc/system/versions.html#order-of-versions URL
- https://security-tracker.debian.org/tracker/CVE-2026-89422 Vendor Advisory
- https://ubuntu.com/security/CVE-2026-89422 Third Party Advisory
- https://www.cve.org/CVERecord?id=CVE-2026-89422 Third Party Advisory
Severity
9.1
Critical
CVSS 4.0: 9.3 (NVD)
Exploitation
EPSS <1%
Type
CWE-322Key Exchange without Entity Authentication
Timeline
Published22 Sep 2026
Updated23 Sep 2026
First seen22 Sep 2026
Sources
CVE-2026-89422 · NVD
CVE-2026-89422 · MITRE
EEF-CVE-2026-89422 · OSV
GHSA-rgxr-4g4w-j875 · GHSA
DEBIAN-CVE-2026-89422 · OSV
UBUNTU-CVE-2026-89422 · OSV
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