Description
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.
Published: 2026-07-02
Score: 8.7 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

A Time-of-Check Time-of-Use (TOCTOU) race condition in the Erlang/OTP SSL DTLS demultiplexer allows an unauthenticated remote attacker to crash the shared demux process, causing all active DTLS sessions on the listener to terminate and resulting in a denial of service. The flaw is a classic availability weakness, classified as CWE‑367.

Affected Systems

The flaw affects Erlang:OTP releases 25.3 up to but not including 29.0.3, 28.5.0.3, and 27.3.4.14. The corresponding SSL libraries affected are 10.9 up to but not including 11.7.3, 11.6.0.3, and 11.2.12.10 respectively. The fault lies in lib/ssl/src/dtls_packet_demux.erl and impacts any DTLS server listener that uses a single shared demux process to route UDP packets.

Risk and Exploitability

The CVSS score of 8.7 signals high severity, and the EPSS score of < 1% indicates a very low probability of exploitation. The vulnerability is not listed in the CISA KEV catalog. Based on the description, it is inferred that the attack vector is remote network via UDP, as the attacker needs only to send ClientHello packets from the same source IP and port. No authentication or special configuration is required, making the exploit trivial for an attacker with UDP connectivity to the listener. Because the crash can be repeated indefinitely, the risk to all clients of the affected listener is high.

Generated by OpenCVE AI on July 22, 2026 at 13:27 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade Erlang/OTP to 29.0.3 or later, which incorporates the dtls_packet_demux race condition fix.
  • Configure firewalls or network devices to limit the rate of DTLS ClientHello packets from a single source IP and port, preventing repeated rapid packets that trigger the race condition.
  • If upgrading immediately is not feasible, replace the built-in DTLS implementation with an alternative that does not rely on a shared demux process, or modify the application to isolate each DTLS session, thereby preventing a single point of failure.

Generated by OpenCVE AI on July 22, 2026 at 13:27 UTC.

Tracking

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Advisories

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History

Thu, 02 Jul 2026 21:00:00 +0000

Type Values Removed Values Added
First Time appeared Erlang erlang/otp
Erlang otp
Vendors & Products Erlang erlang/otp
Erlang otp

Thu, 02 Jul 2026 18:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Thu, 02 Jul 2026 16:45:00 +0000

Type Values Removed Values Added
Description 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.
Title DTLS listener crash via race condition in dtls_packet_demux causes denial of service for all sessions
First Time appeared Erlang
Erlang erlang\/otp
Weaknesses CWE-367
CPEs cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
Vendors & Products Erlang
Erlang erlang\/otp
References
Metrics cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}

Subscriptions

Erlang Erlang/otp Erlang\/otp Otp
cve-icon MITRE

Status: PUBLISHED

Assigner: EEF

Published:

Updated: 2026-07-03T04:29:33.147Z

Reserved: 2026-06-17T17:55:15.685Z

Link: CVE-2026-55950

cve-icon Vulnrichment

Updated: 2026-07-02T17:25:49.598Z

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-07-22T13:30:05Z

Weaknesses
  • CWE-367

    Time-of-check Time-of-use (TOCTOU) Race Condition