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CVE-2026-55950— DTLS listener crash via race condition in dtls_packet_demux causes denial of service for all sessions

Quick assessment

Affected
Erlang OTP
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

erlang erlang/otp是erlang社区开源的一套并发编程语言及运行时系统。 Erlang/OTP存在竞争条件问题漏洞，该漏洞源于ssl的dtls_packet_demux模块存在Time-of-check Time-of-use (TOCTOU)竞争条件问题，可能导致未经身份验证的远程攻击者崩溃监听器上所有活动的DTLS会话。

CVSS 8.7 · High EPSS 0.38% · P30

Affected Version Matrix 3

VendorProduct Version RangeStatus
Erlang OTP 10.9< * affected
25.3< * affected
44dcb4c3d900777493ce2a6129f451aa475811f9< e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04 affected
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I. Basic Information for CVE-2026-55950

Vulnerability Information
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Vulnerability Title
DTLS listener crash via race condition in dtls_packet_demux causes denial of service for all sessions
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
检查时间与使用时间(TOCTOU)的竞争条件
Source: CVE Program / CVE List V5
Vulnerability Title
Erlang/OTP 竞争条件问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
erlang erlang/otp是erlang社区开源的一套并发编程语言及运行时系统。 Erlang/OTP存在竞争条件问题漏洞，该漏洞源于ssl的dtls_packet_demux模块存在Time-of-check Time-of-use (TOCTOU)竞争条件问题，可能导致未经身份验证的远程攻击者崩溃监听器上所有活动的DTLS会话。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Erlang OTP 10.9 ~ * cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
Erlang OTP 25.3 ~ * cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-55950

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III. Intelligence Information for CVE-2026-55950

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Patches & Fixes for CVE-2026-55950 (1)

Vendor Advisories for CVE-2026-55950 (3)

Same Patch Batch · Erlang · 2026-07-02 · 6 CVEs total

CVE-2026-55952 8.2 HIGH TLS 1.3 server denial of service via malformed ClientHello pre-shared key extension
CVE-2026-54887 6.3 MEDIUM DTLS server cookie bypass during startup window due to empty initial cookie secret
CVE-2026-54891 6.3 MEDIUM Plaintext APPLICATION_DATA injected during TLS handshake delivered to client application p
CVE-2026-54886 5.3 MEDIUM SSH SFTP server denial of service via extended channel data infinite loop
CVE-2026-53422 2.3 LOW SFTP REALPATH path-existence oracle allowing filesystem enumeration outside configured roo

IV. Related Vulnerabilities

Same product: OTP
Same vendor: Erlang
Same weakness: CWE-367

V. Comments for CVE-2026-55950

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