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🛡️ CVE-2026-55950 — otp

🟡 CVSS 5.9 — Medium ✅ No Known Exploit CWE-367 NVD
5.9
CVSS Score
0 Low4 Medium7 High9 Critical10

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 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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: High — the attacker first has to win a race, learn a secret or otherwise prepare the target.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-55950 is classified as CWE-367: Time-of-check Time-of-use Race Condition. The state checked and the state acted upon can differ, because it may change between the two steps.

Affected software

CVE-2026-55950 is recorded against 2 packages.

  • erlang\/otp (from 29.0 up to 29.0.3)
  • erlang\/ssl (from 11.7 up to 11.7.3)

Timeline and source

Published on 2 July 2026 and last revised on 24 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

cna.erlef.org
github.com
github.com
osv.dev
www.erlang.org

Other advisories for this package

erlang\/otp has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-367: Time-of-check Time-of-use Race Condition) in other software:

Details

Severity MEDIUM
CVSS Score 5.9
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-367
Public Exploit ✅ No
Source NVD
Published 2026-07-02
Updated 2026-08-20
Modified 2026-07-24

Affected Packages

Software From version Fixed in
erlang\/otp 29.0 29.0.3
erlang\/ssl 11.7 11.7.3

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