DTLS listener crash via race condition in dtls_packet_demux causes denial of service for all sessions

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-55950
StatePUBLISHED
AssignerEEF
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-02 17:17:02 UTC
Updated2026-07-07 14:45:59 UTC
DescriptionTime-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.

Risk And Classification

Primary CVSS: v4.0 8.7 HIGH from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS: 0.004060000 probability, percentile 0.325570000 (date 2026-07-05)

Problem Types: CWE-367 | CWE-367 CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

VersionSourceTypeScoreSeverityVector
4.06b3ad84c-e1a6-4bf7-a703-f496b71e49dbSecondary8.7HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/C...
4.0CNACVSS8.7HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
3.1[email protected]Primary5.9MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
None
Integrity
None
Availability
High
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Erlang Erlang/otp All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Erlang OTP affected 10.9 * otp Not specified
CNA Erlang OTP affected 25.3 * otp Not specified
CNA Erlang OTP affected 44dcb4c3d900777493ce2a6129f451aa475811f9 e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04 git Not specified

References

ReferenceSourceLinkTags
github.com/erlang/otp/commit/e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04 6b3ad84c-e1a6-4bf7-a703-f496b71e49db github.com Patch
github.com/erlang/otp/security/advisories/GHSA-hwfc-5hf4-gvr3 6b3ad84c-e1a6-4bf7-a703-f496b71e49db github.com Vendor Advisory
cna.erlef.org/cves/CVE-2026-55950.html 6b3ad84c-e1a6-4bf7-a703-f496b71e49db cna.erlef.org Vendor Advisory
www.erlang.org/doc/system/versions.html 6b3ad84c-e1a6-4bf7-a703-f496b71e49db www.erlang.org Release Notes
osv.dev/vulnerability/EEF-CVE-2026-55950 6b3ad84c-e1a6-4bf7-a703-f496b71e49db osv.dev Third Party Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Lukas Backström (en)

CNA: Ingela Anderton Andin (en)

CNA: Dan Gudmundsson (en)

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