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VulnerabilityPublished Updated

CVE-2026-55950: Erlang OTP · Time-of-check Time-of-use (TOCTOU) Race Condition

Affects Erlang OTPSource CVE Database V5

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Not known to be exploited · CVSS 8.7 High : upgrade to e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04 soon.

Data as of 14 Nov 2026, 20:58 UTC

CVSS 4.0 base score
8.7High
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (EEF)CVSS 4.08.7
EPSS
0.4% chance of exploitation in 30 days – higher than 34% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04, 11.2.12.10
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

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 2 Jul 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 14 Nov 2026.

What to do

Upgrade OTP to e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04; ssl to 11.2.12.10.

Affected software

ProductAffectedFixed in
OTPotpAffected
  • >=25.3 <27.3.4.14
Fixed in–
OTPsslAffected
  • >=10.9 <11.2.12.10
Fixed in–
OTPerlang/otpAffected
  • ≥ 44dcb4c3d900777493ce2a6129f451aa475811f9, < e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04
Fixed in
  • e44d2bf01c4473ef2ea7f09e3523cf96de6e4a04
GitHubsslpkg:github/sslOther threatsAffected
  • >=10.9 <11.2.12.10
Fixed in
  • 11.2.12.10

CPE configurations (1)

  • cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

If you cannot patch yet, consider mitigating by limiting rapid reconnections from the same source IP and port if possible, though no specific vendor guidance is given.

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 27.3.4.14, OTP 28.5.0.3, and OTP 29.0.3, corresponding to ssl from 10.9 before 11.2.12.10, 11.6.0.3, and 11.7.3.

References

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