CVE-2026-56812: Improper Check for Unusual or Exceptional Conditions vulnerability in phoenixframework phoenix (Presence JavaS

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-56812 is a high-severity flaw (CVSS 7.5) affecting phoenix. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Improper Check for Unusual or Exceptional Conditions vulnerability in phoenixframework phoenix (Presence JavaScript client) allows an attacker with ordinary channel access to cause a persistent client-side denial of service against every viewer of a presence channel topic. This vulnerability is associated with program files assets/js/phoenix/presence.js and program routines Presence.syncState and Presence.syncDiff. The Phoenix JavaScript presen

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.8% (top 44%)
CISA exploited list	No
Weakness	CWE-754
Published	2026-07-07
Last modified	2026-10-25

Publisher (CNA): EEF · Vendor: phoenixframework

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

Am I affected?

Timeline

2026-07-07 16:16 UTCPublished CVE record published
2026-10-25 20:10 UTCUpdated Record last modified

phoenixframework phoenix UPGRADE

Affected: >= 1.2.0 and < 1.5.15 · >= 1.6.0 and < 1.6.17 · >= 1.7.0 and < 1.7.24 · >= 1.8.0 and < 1.8.9

Fixed in: 1.5.15, 1.6.17, 1.7.24, 1.8.9

Safe to downgrade to: a release before 1.2.0

1. Check installed version

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

2. UPGRADE to 1.5.15 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade phoenix

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 1.2.0 (Debian / Ubuntu)

apt-cache madison phoenix sudo apt install phoenix=<VERSION_BEFORE_1.2.0> sudo apt-mark hold phoenix

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

dnf --showduplicates list phoenix sudo dnf downgrade phoenix-<VERSION_BEFORE_1.2.0> sudo dnf versionlock add phoenix

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.

Exact fixes by distribution

npm · phoenix · FIXED · 1.5.15 · vulnerable: >= 1.2.0-rc.0, < 1.5.15 · source

npm install phoenix@">=1.5.15" npm ls phoenix

Fedora 46 · python-apprise · FIXED · 2.1.0-1.fc46 · FEDORA-2026-ef67a72c5d · source

sudo dnf upgrade --advisory=FEDORA-2026-ef67a72c5d

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: cna.erlef.org/cves/CVE-2026-56812.html
Write-up: github.com/phoenixframework/phoenix/security/advisories/GHSA-63mc-hw7g-86rr

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-2026-56812?

phoenix: upgrade to 1.5.15, 1.6.17, 1.7.24, 1.8.9. Exact commands for each OS are on this page.

Is CVE-2026-56812 being exploited?

CVE-2026-56812 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-2026-56812 affect?

CVE-2026-56812 affects phoenix. Severity is high (CVSS 7.5). Improper Check for Unusual or Exceptional Conditions vulnerability in phoenixframework phoenix (Presence JavaScript client) allows an attacker with ordinary channel access to cause a persistent client-side denial of service against every vi

How urgent is CVE-2026-56812?

Priority 50/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-56811 HIGH 7.5 UPGRADE Allocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (Phoenix.Socket

References

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