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Fencer Vulns
high 7.4

CVE-2026-55953 json

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

published 2026-07-27 3 mo ago modified 2026-10-24 16 d ago also EUVD-2026-49323

cvss
7.4
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 14%
public exploits
0
none known

Summary

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.

Patch / fix

  • Erlang OTP 11.2.12.11, 11.6.0.4, 11.7.4, 27.3.4.15, 28.5.0.4, 29.0.4
  • erlang Debian 13 1:27.3.4.1+dfsg-1+deb13u3
  • erlang Debian 14 1:29.0.4+dfsg-1

debian advisories DEBIAN-CVE-2026-55953

  • erlang Ubuntu 22.04 LTS 1:24.2.1+dfsg-1ubuntu0.7
  • erlang Ubuntu 24.04 LTS 1:25.3.2.8+dfsg-1ubuntu4.7
  • erlang Ubuntu 26.04 LTS 1:27.3.4.6+dfsg-1ubuntu0.1
  • erlang Ubuntu Pro 14.04 LTS 1:16.b.3-dfsg-1ubuntu2.2+esm2
  • erlang Ubuntu Pro 16.04 LTS 1:18.3-dfsg-1ubuntu3.1+esm3
  • erlang Ubuntu Pro 18.04 LTS 1:20.2.2+dfsg-1ubuntu2+esm3
  • erlang Ubuntu Pro 20.04 LTS 1:22.2.7+dfsg-1ubuntu0.5+esm2

ubuntu advisories UBUNTU-CVE-2026-55953

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • erlang27 hummingbird 1 27.3.4.15-0.1.hum1
  • erlang27-et hummingbird 1 27.3.4.15-0.1.hum1
  • erlang27-wx hummingbird 1 27.3.4.15-0.1.hum1
  • erlang27-ftp hummingbird 1 27.3.4.15-0.1.hum1
  • erlang27-ssh hummingbird 1 27.3.4.15-0.1.hum1
  • erlang27-ssl hummingbird 1 27.3.4.15-0.1.hum1
  • erlang27-asn1 hummingbird 1 27.3.4.15-0.1.hum1
  • erlang27-edoc hummingbird 1 27.3.4.15-0.1.hum1

red hat advisories RHSA-2026:47009

  • erlang SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 23.3.4.19-150300.3.39.1
  • erlang26 SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Server Applications 15 SP7 26.2.1-150300.7.28.1

suse advisories SUSE-SU-2026:3645-1SUSE-SU-2026:3579-1

  • erlang openSUSE Tumbleweed 28.5.0.4-1.1
  • erlang27 openSUSE Tumbleweed 27.1.3-3.1

opensuse advisories openSUSE-SU-2026:11559-1openSUSE-SU-2026:11560-1

  • erlang Azure Linux 3.0 26.2.5.21-4

azure linux advisories AZL-94196

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-55953 updated cvss 7.4

erlang/otp: Erlang/OTP ssl client: Authentication bypass via unoffered anonymous cipher suite acceptance

  • Red Hat OpenStack Platform 16.2 erlang, erlang-ssl, erlang-asn1, erlang-erts, erlang-hipe, erlang-sasl, +15 more Red Hat OpenStack Platform 17.1 erlang-ssl, erlang-asn1, erlang-erts, erlang-sasl, erlang-snmp, erlang-eldap, +13 more Red Hat OpenStack Platform 18.0 erlang
    affected: workaround, no fix available
  • Red Hat Hardened Images erlang27 27.3.4.15-0.1.hum1
    fixed: vendor fix RHSA-2026:47009

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
3 mo ago

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 9.1 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
CNA 4.0 9.1 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
NVD 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

  • Erlang OTP

Classification

Weakness
  • CWE-757 Selection of Less-Secure Algorithm During Negotiation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.