CVE-2026-55953
Description
A flaw was found in the Erlang/OTP ssl client. This vulnerability allows an on-path attacker to bypass server authentication in TLS 1.2 (and earlier) and DTLS connections. By tricking the client into accepting an unoffered anonymous cipher suite, the attacker can complete the handshake without a valid server certificate. This enables the attacker to read and modify all subsequent application traffic, leading to significant information disclosure and integrity compromise.
Statement
Red Hat rates this flaw as Important (CVSS 7.4), lower than the CVE description alone might suggest, because successful exploitation requires an on-path (man-in-the-middle) attacker positioned between the affected Erlang/OTP TLS client and its intended server. Per CVSS scoring guidance, this network-positioning requirement is scored as Attack Complexity High. Clients that only negotiate TLS 1.3 are not affected, as the TLS 1.3 client handshake path independently validates the negotiated cipher suite.
Mitigation
Clients using only TLS 1.3 are not affected; the TLS 1.3 client handshake path validates the negotiated cipher suite. As a workaround for TLS 1.2/DTLS clients prior to upgrading, explicitly disable anonymous cipher suites (TLS_DH_anon_*, TLS_ECDH_anon_*) in the ssl client configuration, or restrict the client to TLS 1.3-only.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.4 | 7.4 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Red Hat CVSS v3 Score Explanation
Corrected AC:L -> AC:H. Flaw requires an on-path (man-in-the-middle) attacker per the description ("An on-path attacker between the client and the intended server can respond with a ServerHello..."). Per the FIRST CVSS v3.1 specification, injecting oneself into the logical network path to read/modify network communications is the canonical example given for Attack Complexity: High. CVEORG independently corroborates this via their CVSS 4.0 vector using AT:P (Attack Requirements: Present), the v4.0 metric equivalent for this exact on-path condition, which the RH v3.1 vector had not reflected. Corrected score 9.1 -> 7.4 (Critical -> Important).
Understanding the Weakness (CWE)
Access Control,Other
Technical Impact: Gain Privileges or Assume Identity; Varies by Context; Bypass Protection Mechanism
An attacker can access any functionality that is inadvertently accessible to the source.
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