CVE-2026-55950: Time-of-check Time-of-use (TOCTOU) race condition vulnerability in Erlang/OTP ssl (dtls_packet_demux module) a

Routine

MEDIUM 5.9REMOTEUPGRADEUPGRADE

CVE-2026-55950 is a medium-severity flaw (CVSS 5.9) affecting erlang\/otp, erlang\/ssl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 ClientH

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 68%)
CISA exploited list	No
Weakness	CWE-367
Published	2026-07-02
Last modified	2026-10-25

Publisher (CNA): EEF · Vendor: erlang

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-02 17:17 UTCPublished CVE record published
2026-10-25 21:10 UTCUpdated Record last modified

erlang erlang\/otp UPGRADE

Affected: >= 25.3 and < 27.3.4.14 · >= 28.0 and < 28.5.0.3 · >= 29.0 and < 29.0.3

Fixed in: 27.3.4.14, 28.5.0.3, 29.0.3

Safe to downgrade to: a release before 25.3

1. Check installed version

apt-cache policy erlangotp || rpm -q erlangotp || erlangotp --version

2. UPGRADE to 27.3.4.14 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade erlangotp

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade erlangotp

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 25.3 (Debian / Ubuntu)

apt-cache madison erlangotp sudo apt install erlangotp=<VERSION_BEFORE_25.3> sudo apt-mark hold erlangotp

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list erlangotp sudo dnf downgrade erlangotp-<VERSION_BEFORE_25.3> sudo dnf versionlock add erlangotp

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

erlang erlang\/ssl UPGRADE

Affected: >= 10.9 and < 11.2.12.10 · >= 11.3 and < 11.6.0.3 · >= 11.7 and < 11.7.3

Fixed in: 11.2.12.10, 11.6.0.3, 11.7.3

Safe to downgrade to: a release before 10.9

1. Check installed version

apt-cache policy erlangssl || rpm -q erlangssl || erlangssl --version

2. UPGRADE to 11.2.12.10 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade erlangssl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade erlangssl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 10.9 (Debian / Ubuntu)

apt-cache madison erlangssl sudo apt install erlangssl=<VERSION_BEFORE_10.9> sudo apt-mark hold erlangssl

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list erlangssl sudo dnf downgrade erlangssl-<VERSION_BEFORE_10.9> sudo dnf versionlock add erlangssl

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-55950?

erlang\/otp: upgrade to 27.3.4.14, 28.5.0.3, 29.0.3; erlang\/ssl: upgrade to 11.2.12.10, 11.6.0.3, 11.7.3. Exact commands for each OS are on this page.

Is CVE-2026-55950 being exploited?

CVE-2026-55950 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-55950 affect?

CVE-2026-55950 affects erlang\/otp, erlang\/ssl. Severity is medium (CVSS 5.9). 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 sh

How urgent is CVE-2026-55950?

Priority 34/100. Remotely exploitable, no login, no user action

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References

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