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CVE PROGRAM SOURCE RECORD9.1 Critical

CVE-2026-55953

TLS 1.2 and DTLS client accepts unoffered anonymous cipher suite, bypassing server authentication

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Status
Published
Published
Updated
Assigning organization
EEF

Description

The Erlang/OTP ssl TLS 1.2 (and earlier) and DTLS client does not verify that the cipher suite selected by the server in ServerHello was among the suites offered by the client in ClientHello. The client-side tls_handshake:hello/5 handler validates the negotiated protocol version and the downgrade sentinel but hands the server-chosen suite directly to ssl_handshake:handle_server_hello_extensions/9, which installs it without a membership check. The TLS 1.3 client path performs this check (per RFC 8446), so it is not affected. An on-path attacker between the client and the intended server can respond with a ServerHello selecting an anonymous key exchange suite such as TLS_DH_anon_* or TLS_ECDH_anon_* that the client never offered. Anonymous suites do not require the server to present a certificate, so the entire verify_peer and cacerts configuration is bypassed: the attacker completes the handshake with its own ephemeral parameters, no certificate is validated, no hostname is checked, and ssl:connect returns {ok, Socket}. All subsequent application traffic is readable and modifiable by the attacker. This issue affects OTP from OTP 17.0 before OTP 27.3.4.15, from OTP 28.0 before OTP 28.5.0.4, and from OTP 29.0 before OTP 29.0.4, corresponding to ssl from 5.3.4 before 11.2.12.11, from 11.3 before 11.6.0.4, and from 11.7 before 11.7.4. Whether OTP before OTP 17.0, corresponding to ssl before 5.3.4, is affected is unknown.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Erlang OTP

Default version status: unaffected

  • 0 to < 17.0unknown
  • 17.0 to < 27.3.4.15affected
  • 28.0 to < 28.5.0.4affected
  • 29.0 to < 29.0.4affected
pkg:software-id/erlang.org/otp

Erlang OTP

Default version status: unaffected

  • 0 to < 5.3.4unknown
  • 5.3.4 to < 11.2.12.11affected
  • 11.3 to < 11.6.0.4affected
  • 11.7 to < 11.7.4affected
pkg:otp/ssl?repository_url=https:%2F%2Fgithub.com%2Ferlang%2Fotp&vcs_url=git%2Bhttps:%2F%2Fgithub.com%2Ferlang%2Fotp.git

Erlang OTP

Default version status: unaffected

  • 84adefa331c4159d432d22840663c38f155cd4c1 to < *affected
pkg:github/erlang/otp

References