FKIE_CVE-2026-56812
Vulnerability from fkie_nvd - Published: 2026-07-07 16:16 - Updated: 2026-07-08 15:01
Severity
Summary
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 presence client checks whether a presence already exists with a bare truthiness test (state[key]) instead of an own-property check. Presence keys can be attacker-controlled, because applications track presences under a username or id supplied by the client. A user who joins a channel choosing a key that is an Object.prototype member name (__proto__, constructor, toString, hasOwnProperty, and similar) makes that lookup return JavaScript's built-in Object.prototype instead of undefined. Because the prototype is truthy, the code treats it as an existing presence and reads .metas.map(...) off it, which throws an uncaught TypeError.
The exception propagates out of the presence message handler, so the local state is never updated and onSync() never fires. Because the malicious key is tracked on the server, it is re-pushed on every presence update and keeps re-throwing, so presence sync stays broken for every viewer of that channel topic until the attacker leaves. Both syncState and syncDiff use the same unsafe existence-check pattern. The impact is limited to the affected topic and is a read-time confusion of the prototype object, not a mutation of Object.prototype (it is not prototype pollution).
This issue affects phoenix: from 1.2.0-rc.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9.
References
Impacted products
| Vendor | Product | Version |
|---|
{
"affected": [
{
"affectedData": [
{
"collectionURL": "https://repo.hex.pm",
"cpes": [
"cpe:2.3:a:phoenixframework:phoenix:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"Presence"
],
"packageName": "phoenix",
"packageURL": "pkg:hex/phoenix",
"product": "phoenix",
"programFiles": [
"assets/js/phoenix/presence.js"
],
"programRoutines": [
{
"name": "Presence.syncState"
},
{
"name": "Presence.syncDiff"
}
],
"repo": "https://github.com/phoenixframework/phoenix",
"vendor": "phoenixframework",
"versions": [
{
"lessThan": "1.5.15",
"status": "affected",
"version": "1.2.0-rc.0",
"versionType": "semver"
},
{
"lessThan": "1.6.17",
"status": "affected",
"version": "1.6.0-rc.0",
"versionType": "semver"
},
{
"lessThan": "1.7.24",
"status": "affected",
"version": "1.7.0-rc.0",
"versionType": "semver"
},
{
"lessThan": "1.8.9",
"status": "affected",
"version": "1.8.0-rc.0",
"versionType": "semver"
}
]
},
{
"collectionURL": "https://registry.npmjs.org",
"cpes": [
"cpe:2.3:a:phoenixframework:phoenix:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"Presence"
],
"packageName": "phoenix",
"packageURL": "pkg:npm/phoenix",
"product": "phoenix",
"programFiles": [
"assets/js/phoenix/presence.js"
],
"programRoutines": [
{
"name": "Presence.syncState"
},
{
"name": "Presence.syncDiff"
}
],
"repo": "https://github.com/phoenixframework/phoenix",
"vendor": "phoenixframework",
"versions": [
{
"lessThan": "1.5.15",
"status": "affected",
"version": "1.2.0-rc.0",
"versionType": "semver"
},
{
"lessThan": "1.6.17",
"status": "affected",
"version": "1.6.0-rc.0",
"versionType": "semver"
},
{
"lessThan": "1.7.24",
"status": "affected",
"version": "1.7.0-rc.0",
"versionType": "semver"
},
{
"lessThan": "1.8.9",
"status": "affected",
"version": "1.8.0-rc.0",
"versionType": "semver"
}
]
},
{
"collectionURL": "https://github.com",
"cpes": [
"cpe:2.3:a:phoenixframework:phoenix:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"Presence"
],
"packageName": "phoenixframework/phoenix",
"packageURL": "pkg:github/phoenixframework/phoenix",
"product": "phoenix",
"programFiles": [
"assets/js/phoenix/presence.js"
],
"programRoutines": [
{
"name": "Presence.syncState"
},
{
"name": "Presence.syncDiff"
}
],
"repo": "https://github.com/phoenixframework/phoenix",
"vendor": "phoenixframework",
"versions": [
{
"changes": [
{
"at": "7f7b971c1ea0994e3fbd1c11ddb05e780bd38ad8",
"status": "unaffected"
},
{
"at": "89a1c4be161e436241e12b2378a719904b9bd96f",
"status": "unaffected"
},
{
"at": "b90b22521465ece00eb5a19d5aa2b9465b209c85",
"status": "unaffected"
},
{
"at": "beffc4da1e787e572121f68902c63daf4fe7d9c2",
"status": "unaffected"
}
],
"lessThan": "*",
"status": "affected",
"version": "2270aaf21bd02c6a6a1022820564efb605a97655",
"versionType": "git"
}
]
}
],
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "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.\n\nThis vulnerability is associated with program files assets/js/phoenix/presence.js and program routines Presence.syncState and Presence.syncDiff.\n\nThe Phoenix JavaScript presence client checks whether a presence already exists with a bare truthiness test (state[key]) instead of an own-property check. Presence keys can be attacker-controlled, because applications track presences under a username or id supplied by the client. A user who joins a channel choosing a key that is an Object.prototype member name (__proto__, constructor, toString, hasOwnProperty, and similar) makes that lookup return JavaScript\u0027s built-in Object.prototype instead of undefined. Because the prototype is truthy, the code treats it as an existing presence and reads .metas.map(...) off it, which throws an uncaught TypeError.\n\nThe exception propagates out of the presence message handler, so the local state is never updated and onSync() never fires. Because the malicious key is tracked on the server, it is re-pushed on every presence update and keeps re-throwing, so presence sync stays broken for every viewer of that channel topic until the attacker leaves. Both syncState and syncDiff use the same unsafe existence-check pattern. The impact is limited to the affected topic and is a read-time confusion of the prototype object, not a mutation of Object.prototype (it is not prototype pollution).\n\nThis issue affects phoenix: from 1.2.0-rc.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9."
}
],
"id": "CVE-2026-56812",
"lastModified": "2026-07-08T15:01:22.897",
"metrics": {
"cvssMetricV40": [
{
"cvssData": {
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"attackComplexity": "LOW",
"attackRequirements": "PRESENT",
"attackVector": "NETWORK",
"availabilityRequirement": "NOT_DEFINED",
"baseScore": 6.3,
"baseSeverity": "MEDIUM",
"confidentialityRequirement": "NOT_DEFINED",
"exploitMaturity": "NOT_DEFINED",
"integrityRequirement": "NOT_DEFINED",
"modifiedAttackComplexity": "NOT_DEFINED",
"modifiedAttackRequirements": "NOT_DEFINED",
"modifiedAttackVector": "NOT_DEFINED",
"modifiedPrivilegesRequired": "NOT_DEFINED",
"modifiedSubAvailabilityImpact": "NOT_DEFINED",
"modifiedSubConfidentialityImpact": "NOT_DEFINED",
"modifiedSubIntegrityImpact": "NOT_DEFINED",
"modifiedUserInteraction": "NOT_DEFINED",
"modifiedVulnAvailabilityImpact": "NOT_DEFINED",
"modifiedVulnConfidentialityImpact": "NOT_DEFINED",
"modifiedVulnIntegrityImpact": "NOT_DEFINED",
"privilegesRequired": "NONE",
"providerUrgency": "NOT_DEFINED",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"valueDensity": "NOT_DEFINED",
"vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/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",
"version": "4.0",
"vulnAvailabilityImpact": "LOW",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "NONE",
"vulnerabilityResponseEffort": "NOT_DEFINED"
},
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"type": "Secondary"
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"id": "CVE-2026-56812",
"options": [
{
"exploitation": "poc"
},
{
"automatable": "no"
},
{
"technicalImpact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-07-07T16:11:03.353715Z",
"version": "2.0.3"
}
}
]
},
"published": "2026-07-07T16:16:40.920",
"references": [
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://cna.erlef.org/cves/CVE-2026-56812.html"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/phoenixframework/phoenix/commit/7f7b971c1ea0994e3fbd1c11ddb05e780bd38ad8"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/phoenixframework/phoenix/commit/89a1c4be161e436241e12b2378a719904b9bd96f"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/phoenixframework/phoenix/commit/b90b22521465ece00eb5a19d5aa2b9465b209c85"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/phoenixframework/phoenix/commit/beffc4da1e787e572121f68902c63daf4fe7d9c2"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://github.com/phoenixframework/phoenix/security/advisories/GHSA-63mc-hw7g-86rr"
},
{
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-56812"
},
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"url": "https://github.com/phoenixframework/phoenix/security/advisories/GHSA-63mc-hw7g-86rr"
}
],
"sourceIdentifier": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"vulnStatus": "Awaiting Analysis",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-754"
}
],
"source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"type": "Secondary"
}
]
}
Loading…
Loading…
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Loading…
Loading…