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Erlang/OTP CVE-2026-55950

| EUVDEUVD-2026-41414 HIGH
Time-of-check Time-of-use (TOCTOU) Race Condition (CWE-367)
2026-07-02 EEF
Denial Of Service Otp Suse
8.7
CVSS 4.0 · Vendor: EEF
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Severity by source

Vendor (EEF) PRIMARY
8.7 HIGH
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
vuln.today AI
7.5 HIGH

Unauthenticated network UDP reach with an easily repeated race gives AV:N/AC:L/PR:N/UI:N; impact is availability-only (A:H) with no confidentiality or integrity loss, scope unchanged.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Primary rating from Vendor (EEF).

CVSS VectorVendor: EEF

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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

1
Analysis Generated
Jul 02, 2026 - 17:20 vuln.today

DescriptionCVE.org

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.

AnalysisAI

Remote denial of service in Erlang/OTP's ssl application (dtls_packet_demux module) lets an unauthenticated attacker crash every active DTLS session on a listener by rapidly reconnecting from the same source IP and port. Because a single shared demux gen_server routes all UDP datagrams for a listener, its TOCTOU-induced crash takes down all clients, not just the attacker's, and can be repeated for a persistent outage. No public exploit is identified at time of analysis, and the issue is not listed in CISA KEV.

Technical ContextAI

Erlang/OTP is the runtime and standard library set behind many messaging, telecom, and middleware systems; its ssl application implements TLS and DTLS. A DTLS server listener multiplexes connectionless UDP traffic through one dtls_packet_demux gen_server process, which maps client {IP,Port} tuples to per-connection handler processes using an in-memory gb_trees store. The root cause is CWE-367 (Time-of-check Time-of-use race): when a client sends multiple ClientHello messages in quick succession from the same address/port, the demux attempts to insert a key that still exists because the intermediate DOWN monitor message tearing down the prior association has not yet been processed, producing a {key_exists, {old, Client}} error that crashes the gen_server. The bug lives in lib/ssl/src/dtls_packet_demux.erl and is fixed by commit e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04.

RemediationAI

Upgrade Erlang/OTP to a fixed release on your branch: 29.0.3 (ssl 11.7.3), 28.5.0.3 (ssl 11.6.0.3), or 27.3.4.14 (ssl 11.2.12.10); consult the Erlang version-ordering guide (https://www.erlang.org/doc/system/versions.html#order-of-versions) to pick the correct patched build for your major line. The upstream fix is commit e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04, described in advisory GHSA-hwfc-5hf4-gvr3. Where immediate patching is not possible, reduce exposure by restricting UDP access to the DTLS listener port to known/trusted peers via firewall or network ACLs (trade-off: breaks connectivity for legitimate roaming or NAT'd clients whose source ports vary), rate-limiting inbound ClientHello datagrams per source to blunt the rapid-reconnect trigger (trade-off: may drop legitimate fast reconnects), and adding supervision so the demux and listener restart automatically after a crash to shorten outage windows (trade-off: does not prevent the DoS, only limits its duration). None of these workarounds fully closes the race; upgrading is the only complete fix.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Server Applications 15 SP7 Not-Affected
SUSE Linux Enterprise Module for Server Applications 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Not-Affected

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CVE-2026-55950 vulnerability details – vuln.today
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