Erlang OTP up to 10.8/11.7.2/25.2/29.0.2 dtls_packet_demux.erl toctou

Summaryinfo

A vulnerability marked as critical has been reported in Erlang OTP up to 10.8/11.7.2/25.2/29.0.2. This impacts an unknown function in the library lib/ssl/src/dtls_packet_demux.erl. This manipulation causes toctou. This vulnerability is tracked as CVE-2026-55950. The attack is possible to be carried out remotely. No exploit exists. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical was found in Erlang OTP up to 10.8/11.7.2/25.2/29.0.2. Affected by this vulnerability is an unknown code in the library lib/ssl/src/dtls_packet_demux.erl. The manipulation with an unknown input leads to a toctou vulnerability. The CWE definition for the vulnerability is CWE-367. The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check. This can cause the product to perform invalid actions when the resource is in an unexpected state. The impact remains unknown. The summary by CVE 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 29.0.3, 28.5.0.3, and 27.3.4.14 corresponding to ssl from 10.9 before 11.7.3, 11.6.0.3, and 11.2.12.10.

The weakness was disclosed by Lukas Backström. It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-55950 since 06/17/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 10.9, 11.2.12.10, 11.6.0.3, 11.7.3, 25.3, 27.3.4.14, 28.5.0.3 or 29.0.3 eliminates this vulnerability. Applying the patch e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• Erlang

Name

• OTP

Version

• 10.0
• 10.1
• 10.2
• 10.3
• 10.4
• 10.5
• 10.6
• 10.7
• 10.8
• 11.7.0
• 11.7.1
• 11.7.2
• 25.0
• 25.1
• 25.2
• 29.0.0
• 29.0.1
• 29.0.2

Website

• Product: https://github.com/erlang/otp/

CPE 2.3info

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CPE 2.2info

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Entryinfo

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