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 R13B03 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 3.10.7 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 R13B03, corresponding to ssl before 3.10.7, is affected is unknown.
References
| Link | Resource |
|---|---|
| https://cna.erlef.org/cves/CVE-2026-55953.html | Patch Third Party Advisory |
| https://github.com/erlang/otp/commit/064e236414614f9085cbbbd6eacf0e43c02d1b4b | Patch |
| https://github.com/erlang/otp/commit/0a82596d425abe43dc2e0b3d74aa1557ef74051c | Patch |
| https://github.com/erlang/otp/commit/e6ff938116b2872bccc478af7fefb56627285b77 | Patch |
| https://github.com/erlang/otp/security/advisories/GHSA-c6cw-pr89-w882 | Vendor Advisory |
| https://osv.dev/vulnerability/EEF-CVE-2026-55953 | Patch Third Party Advisory |
| https://www.erlang.org/doc/system/versions.html#order-of-versions | Release Notes |
Configurations
Configuration 1 (hide)
|
History
10 Aug 2026, 17:21
| Type | Values Removed | Values Added |
|---|---|---|
| First Time |
Erlang erlang\/ssl
Erlang erlang\/otp Erlang |
|
| CPE | cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:* cpe:2.3:a:erlang:erlang\/ssl:*:*:*:*:*:*:*:* |
|
| References | () https://cna.erlef.org/cves/CVE-2026-55953.html - Patch, Third Party Advisory | |
| References | () https://github.com/erlang/otp/commit/064e236414614f9085cbbbd6eacf0e43c02d1b4b - Patch | |
| References | () https://github.com/erlang/otp/commit/0a82596d425abe43dc2e0b3d74aa1557ef74051c - Patch | |
| References | () https://github.com/erlang/otp/commit/e6ff938116b2872bccc478af7fefb56627285b77 - Patch | |
| References | () https://github.com/erlang/otp/security/advisories/GHSA-c6cw-pr89-w882 - Vendor Advisory | |
| References | () https://osv.dev/vulnerability/EEF-CVE-2026-55953 - Patch, Third Party Advisory | |
| References | () https://www.erlang.org/doc/system/versions.html#order-of-versions - Release Notes | |
| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 7.4 |
03 Aug 2026, 22:16
| Type | Values Removed | Values Added |
|---|---|---|
| Summary | (en) 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 R13B03 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 3.10.7 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 R13B03, corresponding to ssl before 3.10.7, is affected is unknown. |
27 Jul 2026, 16:17
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-07-27 16:17
Updated : 2026-08-10 17:21
NVD link : CVE-2026-55953
Mitre link : CVE-2026-55953
CVE.ORG link : CVE-2026-55953
JSON object : View
Products Affected
erlang
- erlang\/ssl
- erlang\/otp
CWE
CWE-757
Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')