CVE-2026-55950

What it is

Time-of-check Time-of-use (TOCTOU) race condition vulnerability in Erlang/OTP ssl (dtls_packet_demux module) allows an unauthenticated remote attacker to crash all active DTLS sessions on a listener. A DTLS server listener uses a single shared dtls_packet_demux gen_server process to route incoming UDP datagrams to the correct connection handler. When a DTLS client reconnects rapidly from the same source address and port (sending multiple ClientHello messages in quick succession), a race condition in the demux's internal gb_trees key-value store causes a {key_exists, {old, Client}} crash, terminating the demux process. Because the demux is shared across all DTLS associations on that listener, its crash immediately kills every active DTLS session, not just the attacker's. The attack is pre-authentication: the attacker only needs to send UDP datagrams containing valid ClientHello messages from the same source IP and port before the intermediate DOWN monitor message is processed by the gen_server. No credentials, no completed handshake, and no special configuration are required, and the crash can be repeated indefinitely to create a persistent denial of service for all clients of that listener. This vulnerability is associated with program file lib/ssl/src/dtls_packet_demux.erl. This issue affects OTP from OTP 25.3 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssl from 10.9 before 11.7.3, 11.6.0.3 and 11.2.12.10.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

0.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-07-02 17:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-10-25 21:10 UTC Last updatedMost recent change to the record

Details

Published

2026-07-02 17:17 UTC

Last modified

2026-10-25 21:10 UTC

Exploit probability

0.4% · EPSS, next 30 days

Weakness

CWE-367

Record status

Modified

Affected

• Erlang erlang\/otp < 27.3.4.14
• Erlang erlang\/otp < 28.5.0.3
• Erlang erlang\/otp < 29.0.3
• Erlang erlang\/ssl < 11.2.12.10
• Erlang erlang\/ssl < 11.6.0.3
• Erlang erlang\/ssl < 11.7.3

Attack profile CVSS 4.0 · 8.7

Attack vector

Network

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

None

Confidentiality

None

Integrity

None

Availability

High