CVE-2026-65623 (GCVE-0-2026-65623)
Vulnerability from cvelistv5
Published
2026-07-24 16:32
Modified
2026-07-25 04:16
Severity ?
VLAI Severity ?
EPSS score ?
CWE
- CWE-407 - Inefficient Algorithmic Complexity
Summary
Inefficient Algorithmic Complexity vulnerability in mtrudel bandit allows unauthenticated remote denial of service via CPU exhaustion during WebSocket fragment reassembly.
The size guard 'Elixir.Bandit.WebSocket.Connection':oversize_message?/2 called from handle_frame/3 in lib/bandit/websocket/connection.ex appends each non-final continuation frame to a left-nested iolist and then re-measures the entire accumulated buffer with IO.iodata_length/1 on every frame. Because the buffer grows by one element per frame and is fully re-traversed each time, reassembly work is quadratic (O(n^2)) in the number of continuation frames.
The max_fragmented_message_size limit (default 8 MB) bounds total bytes but not frame count, and each frame can carry as little as one payload byte, so an attacker can send millions of tiny continuation frames using modest bandwidth to pin a CPU core for minutes to hours. Many concurrent connections can starve the whole server of CPU, denying service to legitimate users. The WebSocket read timeout does not help, because it is an idle timeout evaluated between reads and cannot preempt the synchronous reassembly work spent inside a single callback.
This issue affects bandit: from 1.11.0 before 1.12.1.
References
| URL | Tags | |
|---|---|---|
Impacted products
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-65623",
"options": [
{
"Exploitation": "poc"
},
{
"Automatable": "yes"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-07-24T17:08:51.111665Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-07-24T17:09:09.552Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"references": [
{
"tags": [
"exploit"
],
"url": "https://github.com/mtrudel/bandit/security/advisories/GHSA-vg8x-66vg-5pxh"
}
],
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"collectionURL": "https://repo.hex.pm",
"cpes": [
"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"Elixir.Bandit.WebSocket.Connection"
],
"packageName": "bandit",
"packageURL": "pkg:hex/bandit",
"product": "bandit",
"programFiles": [
"lib/bandit/websocket/connection.ex"
],
"programRoutines": [
{
"name": "\u0027Elixir.Bandit.WebSocket.Connection\u0027:handle_frame/3"
},
{
"name": "\u0027Elixir.Bandit.WebSocket.Connection\u0027:oversize_message?/2"
}
],
"repo": "https://github.com/mtrudel/bandit",
"vendor": "mtrudel",
"versions": [
{
"lessThan": "1.12.1",
"status": "affected",
"version": "1.11.0",
"versionType": "semver"
}
]
},
{
"collectionURL": "https://github.com",
"cpes": [
"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"
],
"defaultStatus": "unaffected",
"modules": [
"Elixir.Bandit.WebSocket.Connection"
],
"packageName": "mtrudel/bandit",
"packageURL": "pkg:github/mtrudel/bandit",
"product": "bandit",
"programFiles": [
"lib/bandit/websocket/connection.ex"
],
"programRoutines": [
{
"name": "\u0027Elixir.Bandit.WebSocket.Connection\u0027:handle_frame/3"
},
{
"name": "\u0027Elixir.Bandit.WebSocket.Connection\u0027:oversize_message?/2"
}
],
"repo": "https://github.com/mtrudel/bandit",
"vendor": "mtrudel",
"versions": [
{
"lessThan": "418ef7e906192a230ddba112f7a669c87b6b0e3a",
"status": "affected",
"version": "21612c7c7b1ce43eccd36d3af3a2299d23513667",
"versionType": "git"
}
]
}
],
"configurations": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "\u003cp\u003eThis vulnerability only affects applications that serve WebSocket endpoints through Bandit (including Phoenix applications that use Bandit as the HTTP adapter). Applications that do not upgrade any connections to WebSocket are not affected.\u003c/p\u003e"
}
],
"value": "This vulnerability only affects applications that serve WebSocket endpoints through Bandit (including Phoenix applications that use Bandit as the HTTP adapter). Applications that do not upgrade any connections to WebSocket are not affected."
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*",
"versionEndExcluding": "1.12.1",
"versionStartIncluding": "1.11.0",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
],
"operator": "AND"
}
],
"credits": [
{
"lang": "en",
"type": "finder",
"value": "Peter Ullrich"
},
{
"lang": "en",
"type": "remediation developer",
"value": "Mat Trudel"
}
],
"descriptions": [
{
"lang": "en",
"supportingMedia": [
{
"base64": false,
"type": "text/html",
"value": "Inefficient Algorithmic Complexity vulnerability in mtrudel bandit allows unauthenticated remote denial of service via CPU exhaustion during WebSocket fragment reassembly.\u003cp\u003eThe size guard \u003ctt\u003e\u0027Elixir.Bandit.WebSocket.Connection\u0027:oversize_message?/2\u003c/tt\u003e called from \u003ctt\u003ehandle_frame/3\u003c/tt\u003e in \u003ctt\u003elib/bandit/websocket/connection.ex\u003c/tt\u003e appends each non-final continuation frame to a left-nested iolist and then re-measures the entire accumulated buffer with \u003ctt\u003eIO.iodata_length/1\u003c/tt\u003e on every frame. Because the buffer grows by one element per frame and is fully re-traversed each time, reassembly work is quadratic (O(n^2)) in the number of continuation frames.\u003c/p\u003e\u003cp\u003eThe \u003ctt\u003emax_fragmented_message_size\u003c/tt\u003e limit (default 8 MB) bounds total bytes but not frame count, and each frame can carry as little as one payload byte, so an attacker can send millions of tiny continuation frames using modest bandwidth to pin a CPU core for minutes to hours. Many concurrent connections can starve the whole server of CPU, denying service to legitimate users. The WebSocket read timeout does not help, because it is an idle timeout evaluated between reads and cannot preempt the synchronous reassembly work spent inside a single callback.\u003c/p\u003e\u003cp\u003eThis issue affects bandit: from 1.11.0 before 1.12.1.\u003c/p\u003e"
}
],
"value": "Inefficient Algorithmic Complexity vulnerability in mtrudel bandit allows unauthenticated remote denial of service via CPU exhaustion during WebSocket fragment reassembly.\n\nThe size guard \u0027Elixir.Bandit.WebSocket.Connection\u0027:oversize_message?/2 called from handle_frame/3 in lib/bandit/websocket/connection.ex appends each non-final continuation frame to a left-nested iolist and then re-measures the entire accumulated buffer with IO.iodata_length/1 on every frame. Because the buffer grows by one element per frame and is fully re-traversed each time, reassembly work is quadratic (O(n^2)) in the number of continuation frames.\n\nThe max_fragmented_message_size limit (default 8 MB) bounds total bytes but not frame count, and each frame can carry as little as one payload byte, so an attacker can send millions of tiny continuation frames using modest bandwidth to pin a CPU core for minutes to hours. Many concurrent connections can starve the whole server of CPU, denying service to legitimate users. The WebSocket read timeout does not help, because it is an idle timeout evaluated between reads and cannot preempt the synchronous reassembly work spent inside a single callback.\n\nThis issue affects bandit: from 1.11.0 before 1.12.1."
}
],
"impacts": [
{
"capecId": "CAPEC-229",
"descriptions": [
{
"lang": "en",
"value": "CAPEC-229 Serialized Data Parameter Blowup"
}
]
}
],
"metrics": [
{
"cvssV4_0": {
"attackComplexity": "LOW",
"attackRequirements": "NONE",
"attackVector": "NETWORK",
"baseScore": 8.7,
"baseSeverity": "HIGH",
"privilegesRequired": "NONE",
"subAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"userInteraction": "NONE",
"vectorString": "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",
"version": "4.0",
"vulnAvailabilityImpact": "HIGH",
"vulnConfidentialityImpact": "NONE",
"vulnIntegrityImpact": "NONE"
},
"format": "CVSS",
"scenarios": [
{
"lang": "en",
"value": "GENERAL"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-407",
"description": "CWE-407 Inefficient Algorithmic Complexity",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-07-25T04:16:42.726Z",
"orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"shortName": "EEF"
},
"references": [
{
"tags": [
"vendor-advisory",
"related"
],
"url": "https://github.com/mtrudel/bandit/security/advisories/GHSA-vg8x-66vg-5pxh"
},
{
"tags": [
"related"
],
"url": "https://cna.erlef.org/cves/CVE-2026-65623.html"
},
{
"tags": [
"related"
],
"url": "https://osv.dev/vulnerability/EEF-CVE-2026-65623"
},
{
"tags": [
"patch"
],
"url": "https://github.com/mtrudel/bandit/commit/418ef7e906192a230ddba112f7a669c87b6b0e3a"
}
],
"source": {
"discovery": "EXTERNAL"
},
"title": "Quadratic CPU blow-up reassembling fragmented WebSocket messages in Bandit",
"x_generator": {
"engine": "cvelib 1.8.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db",
"assignerShortName": "EEF",
"cveId": "CVE-2026-65623",
"datePublished": "2026-07-24T16:32:24.923Z",
"dateReserved": "2026-07-22T13:55:59.401Z",
"dateUpdated": "2026-07-25T04:16:42.726Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"vulnrichment": {
"containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-65623\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"poc\"}, {\"Automatable\": \"yes\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-07-24T17:08:51.111665Z\"}}}], \"references\": [{\"url\": \"https://github.com/mtrudel/bandit/security/advisories/GHSA-vg8x-66vg-5pxh\", \"tags\": [\"exploit\"]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-07-24T17:09:03.715Z\"}}], \"cna\": {\"title\": \"Quadratic CPU blow-up reassembling fragmented WebSocket messages in Bandit\", \"source\": {\"discovery\": \"EXTERNAL\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"finder\", \"value\": \"Peter Ullrich\"}, {\"lang\": \"en\", \"type\": \"remediation developer\", \"value\": \"Mat Trudel\"}], \"impacts\": [{\"capecId\": \"CAPEC-229\", \"descriptions\": [{\"lang\": \"en\", \"value\": \"CAPEC-229 Serialized Data Parameter Blowup\"}]}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV4_0\": {\"version\": \"4.0\", \"baseScore\": 8.7, \"attackVector\": \"NETWORK\", \"baseSeverity\": \"HIGH\", \"vectorString\": \"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\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"LOW\", \"attackRequirements\": \"NONE\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"NONE\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"HIGH\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"NONE\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"cpes\": [\"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/mtrudel/bandit\", \"vendor\": \"mtrudel\", \"modules\": [\"Elixir.Bandit.WebSocket.Connection\"], \"product\": \"bandit\", \"versions\": [{\"status\": \"affected\", \"version\": \"1.11.0\", \"lessThan\": \"1.12.1\", \"versionType\": \"semver\"}], \"packageURL\": \"pkg:hex/bandit\", \"packageName\": \"bandit\", \"programFiles\": [\"lib/bandit/websocket/connection.ex\"], \"collectionURL\": \"https://repo.hex.pm\", \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"\u0027Elixir.Bandit.WebSocket.Connection\u0027:handle_frame/3\"}, {\"name\": \"\u0027Elixir.Bandit.WebSocket.Connection\u0027:oversize_message?/2\"}]}, {\"cpes\": [\"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*\"], \"repo\": \"https://github.com/mtrudel/bandit\", \"vendor\": \"mtrudel\", \"modules\": [\"Elixir.Bandit.WebSocket.Connection\"], \"product\": \"bandit\", \"versions\": [{\"status\": \"affected\", \"version\": \"21612c7c7b1ce43eccd36d3af3a2299d23513667\", \"lessThan\": \"418ef7e906192a230ddba112f7a669c87b6b0e3a\", \"versionType\": \"git\"}], \"packageURL\": \"pkg:github/mtrudel/bandit\", \"packageName\": \"mtrudel/bandit\", \"programFiles\": [\"lib/bandit/websocket/connection.ex\"], \"collectionURL\": \"https://github.com\", \"defaultStatus\": \"unaffected\", \"programRoutines\": [{\"name\": \"\u0027Elixir.Bandit.WebSocket.Connection\u0027:handle_frame/3\"}, {\"name\": \"\u0027Elixir.Bandit.WebSocket.Connection\u0027:oversize_message?/2\"}]}], \"references\": [{\"url\": \"https://github.com/mtrudel/bandit/security/advisories/GHSA-vg8x-66vg-5pxh\", \"tags\": [\"vendor-advisory\", \"related\"]}, {\"url\": \"https://cna.erlef.org/cves/CVE-2026-65623.html\", \"tags\": [\"related\"]}, {\"url\": \"https://osv.dev/vulnerability/EEF-CVE-2026-65623\", \"tags\": [\"related\"]}, {\"url\": \"https://github.com/mtrudel/bandit/commit/418ef7e906192a230ddba112f7a669c87b6b0e3a\", \"tags\": [\"patch\"]}], \"x_generator\": {\"engine\": \"cvelib 1.8.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"Inefficient Algorithmic Complexity vulnerability in mtrudel bandit allows unauthenticated remote denial of service via CPU exhaustion during WebSocket fragment reassembly.\\n\\nThe size guard \u0027Elixir.Bandit.WebSocket.Connection\u0027:oversize_message?/2 called from handle_frame/3 in lib/bandit/websocket/connection.ex appends each non-final continuation frame to a left-nested iolist and then re-measures the entire accumulated buffer with IO.iodata_length/1 on every frame. Because the buffer grows by one element per frame and is fully re-traversed each time, reassembly work is quadratic (O(n^2)) in the number of continuation frames.\\n\\nThe max_fragmented_message_size limit (default 8 MB) bounds total bytes but not frame count, and each frame can carry as little as one payload byte, so an attacker can send millions of tiny continuation frames using modest bandwidth to pin a CPU core for minutes to hours. Many concurrent connections can starve the whole server of CPU, denying service to legitimate users. The WebSocket read timeout does not help, because it is an idle timeout evaluated between reads and cannot preempt the synchronous reassembly work spent inside a single callback.\\n\\nThis issue affects bandit: from 1.11.0 before 1.12.1.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"Inefficient Algorithmic Complexity vulnerability in mtrudel bandit allows unauthenticated remote denial of service via CPU exhaustion during WebSocket fragment reassembly.\u003cp\u003eThe size guard \u003ctt\u003e\u0027Elixir.Bandit.WebSocket.Connection\u0027:oversize_message?/2\u003c/tt\u003e called from \u003ctt\u003ehandle_frame/3\u003c/tt\u003e in \u003ctt\u003elib/bandit/websocket/connection.ex\u003c/tt\u003e appends each non-final continuation frame to a left-nested iolist and then re-measures the entire accumulated buffer with \u003ctt\u003eIO.iodata_length/1\u003c/tt\u003e on every frame. Because the buffer grows by one element per frame and is fully re-traversed each time, reassembly work is quadratic (O(n^2)) in the number of continuation frames.\u003c/p\u003e\u003cp\u003eThe \u003ctt\u003emax_fragmented_message_size\u003c/tt\u003e limit (default 8 MB) bounds total bytes but not frame count, and each frame can carry as little as one payload byte, so an attacker can send millions of tiny continuation frames using modest bandwidth to pin a CPU core for minutes to hours. Many concurrent connections can starve the whole server of CPU, denying service to legitimate users. The WebSocket read timeout does not help, because it is an idle timeout evaluated between reads and cannot preempt the synchronous reassembly work spent inside a single callback.\u003c/p\u003e\u003cp\u003eThis issue affects bandit: from 1.11.0 before 1.12.1.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-407\", \"description\": \"CWE-407 Inefficient Algorithmic Complexity\"}]}], \"configurations\": [{\"lang\": \"en\", \"value\": \"This vulnerability only affects applications that serve WebSocket endpoints through Bandit (including Phoenix applications that use Bandit as the HTTP adapter). Applications that do not upgrade any connections to WebSocket are not affected.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eThis vulnerability only affects applications that serve WebSocket endpoints through Bandit (including Phoenix applications that use Bandit as the HTTP adapter). Applications that do not upgrade any connections to WebSocket are not affected.\u003c/p\u003e\", \"base64\": false}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"1.12.1\", \"versionStartIncluding\": \"1.11.0\"}], \"operator\": \"OR\"}], \"operator\": \"AND\"}], \"providerMetadata\": {\"orgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"shortName\": \"EEF\", \"dateUpdated\": \"2026-07-25T04:16:42.726Z\"}}}",
"cveMetadata": "{\"cveId\": \"CVE-2026-65623\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-07-25T04:16:42.726Z\", \"dateReserved\": \"2026-07-22T13:55:59.401Z\", \"assignerOrgId\": \"6b3ad84c-e1a6-4bf7-a703-f496b71e49db\", \"datePublished\": \"2026-07-24T16:32:24.923Z\", \"assignerShortName\": \"EEF\"}",
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
Loading…
Loading…
Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
Loading…
Loading…