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Otp CVE-2026-55953

| EUVDEUVD-2026-49323 CRITICAL
Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade') (CWE-757)
2026-07-27 EEF
Authentication Bypass Microsoft Otp Erlang
9.1
CVSS 4.0 · Vendor: EEF
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Severity by source

Vendor (EEF) PRIMARY
9.1 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
SUSE
7.4 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Red Hat
7.4 HIGH
qualitative

Primary rating from Vendor (EEF).

CVSS VectorVendor: EEF

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Source Code Evidence Fetched
Jul 27, 2026 - 15:50 vuln.today
Analysis Generated
Jul 27, 2026 - 15:50 vuln.today
CVE Published
Jul 27, 2026 - 15:21 cve.org
CRITICAL 9.1

DescriptionCVE.org

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 17.0 before 27.3.4.15, 28.5.0.4, and 29.0.4 corresponding to ssl from 5.3.4 before 11.2.12.11, 11.6.0.4, and 11.7.4.

AnalysisAI

An on-path attacker can force an Erlang/OTP TLS 1.2 or DTLS client to accept an anonymous cipher suite not offered by the client, bypassing certificate validation and enabling full traffic decryption and manipulation. This affects OTP versions 17.0 through prior to 27.3.4.15, 28.5.0.4, and 29.0.4. The vulnerability is resolved in patched releases; no active exploitation or public proof-of-concept is known at this time.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Server Applications 15 SP7 Affected
SUSE Linux Enterprise Module for Server Applications 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected

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CVE-2026-55953 vulnerability details – vuln.today
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