CVE-2026-55953: TLS 1.2 and DTLS client accepts unoffered anonymous cipher suite, bypassing server authentication

Critical 9.1 EPSS 0.2% Erlang/OTP

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.

CVE-2026-55953CVE identifier
9.1CVSS 4.0 base score (critical)
0.2%EPSS: chance of exploitation in the next 30 days (higher than 14% of CVEs)
2026-07-27published

What do these terms mean? CVE · CVSS score · exploited (KEV) · EPSS · backported fix · all terms

What to do now

Check whether you run Erlang/OTP and which version (commands below).
Install the fixed version for your system: see “Patch it” below.
Restart every BEAM service (RabbitMQ, ejabberd, CouchDB, Elixir apps)

Affected and fixed versions

Affected:

Erlang OTP 17.0 to before 27.3.4.15
Erlang OTP 28.0 to before 28.5.0.4
Erlang OTP 29.0 to before 29.0.4
Erlang OTP 5.3.4 to before 11.2.12.11
Erlang OTP 11.3 to before 11.6.0.4
Erlang OTP 11.7 to before 11.7.4
Erlang OTP 84adefa331c4159d432d22840663c38f155cd4c1

Patch it

Use the commands for your system. Distribution packages often keep an older version number with the fix backported, so compare with the fixed package versions in the table below, not only with the upstream version.

Debian

sudo apt update
sudo apt install --only-upgrade erlang-base erlang-ssh

Ubuntu

sudo apt update
sudo apt install --only-upgrade erlang-base erlang-ssh

RHEL, AlmaLinux, Rocky, Oracle

not in RHEL/EPEL: Erlang Solutions or RabbitMQ repo

Fedora

sudo dnf upgrade --refresh erlang

SUSE / openSUSE

sudo zypper refresh
sudo zypper update erlang

Amazon Linux

not in distro repos: vendor repository

Arch Linux

sudo pacman -Syu

Alpine

apk update && apk upgrade erlang28 (or erlang27)

FreeBSD

pkg update && pkg upgrade erlang (or erlang-runtime27/28)

General update steps for every system are on the Linux and Unix & BSD pages; after updating, see which services to restart.

Fix status in Linux distributions

Release	Package	Status	Fixed version / advisory
Debian 12	`erlang`	not fixed yet
Debian 13	`erlang`	fixed	`1:27.3.4.1+dfsg-1+deb13u3`
Debian testing	`erlang`	fixed	`1:29.0.4+dfsg-1`

From the Debian security tracker, Ubuntu CVE tracker and Red Hat Security Data API, refreshed every few hours.

Sources

Page generated automatically from official sources on 2026-11-03 18:05 UTC. Always confirm with your vendor's advisory.