Medium
zookeeper — security advisory
An unauthenticated attacker can inject arbitrary fake log lines into Apache ZooKeeper's operational log by sending a crafted add_auth("ensemble", ...) request containing newline characters (\n). When the ensemble name doesn't match, EnsembleAuthenticationProvider.handleAuthentication() logs the raw, unsanitized name via LOG.warn(). Because SLF4J's {} placeholder preserves embedded newlines, the attacker can forge complete log entries — with arbitrary timestamps, log levels, class names, and messages — that are visually indistinguishable from genuine ZooKeeper log output. This issue affects Apache ZooKeeper: from 3.9.0 through 3.9.5, from 3.8.0 through 3.8.6. Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.
- Products
- zookeeper
- Affected versions
- 3.4.10-2, 3.4.10-3, 3.4.13-1, 3.4.13-3, 3.4.13-3build1, 3.4.13-3ubuntu0.1~esm1, 3.4.13-4, 3.4.13-5, 3.4.13-5build1, 3.4.13-5ubuntu0.1, 3.4.13-5ubuntu4, 3.4.13-6ubuntu2, 3.4.13-6ubuntu3, 3.4.13-6ubuntu4, 3.4.13-6ubuntu4.1, 3.4.5+dfsg-1, 3.4.5+dfsg-1ubuntu0.1~esm1, 3.4.5+dfsg-1ubuntu0.1~esm3, 3.4.6-8, 3.4.7-1, 3.4.8-1, 3.4.8-1ubuntu0.1~esm1, 3.4.8-1ubuntu0.1~esm2, 3.8.0-11, 3.9.1-1, 3.9.1-1build1, 3.9.1-1build2, 3.9.3-1build2, 3.9.3-1build3, 3.9.4-1, 3.9.5-1, 3.9.5-2
- Fixed versions
- Not specified
- CVEs
- CVE-2026-84501
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 03:23 UTC · Revision 1
Source evidence
An unauthenticated attacker can inject arbitrary fake log lines into Apache ZooKeeper's operational log by sending a crafted add_auth("ensemble", ...) request containing newline characters (\n). When the ensemble name doesn't match, EnsembleAuthenticationProvider.handleAuthentication() logs the raw, unsanitized name via LOG.warn(). Because SLF4J's {} placeholder preserves embedded newlines, the attacker can forge complete log entries — with arbitrary timestamps, log levels, class names, and messages — that are visually indistinguishable from genuine ZooKeeper log output. This issue affects Apache ZooKeeper: from 3.9.0 through 3.9.5, from 3.8.0 through 3.8.6. Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.
osv:UBUNTU-CVE-2026-84501
zookeeper
Fixed versions: Not specified
zookeeper
Fixed versions: Not specified
zookeeper
Fixed versions: Not specified
zookeeper
Fixed versions: Not specified
zookeeper
Fixed versions: Not specified
zookeeper
Fixed versions: Not specified
zookeeper
Fixed versions: Not specified
zookeeper
Fixed versions: Not specified
Complete source record
{
"id": "65f02b6fdf118eeda82a2af441704fa638624f76637f685346e7f4b303f50220",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-84501",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-84501",
"summary": "An unauthenticated attacker can inject arbitrary fake log lines into Apache ZooKeeper's operational log by sending a crafted add_auth(\"ensemble\", ...) request containing newline characters (\\n). When the ensemble name doesn't match, EnsembleAuthenticationProvider.handleAuthentication() logs the raw, unsanitized name via LOG.warn(). Because SLF4J's {} placeholder preserves embedded newlines, the attacker can forge complete log entries — with arbitrary timestamps, log levels, class names, and messages — that are visually indistinguishable from genuine ZooKeeper log output. This issue affects Apache ZooKeeper: from 3.9.0 through 3.9.5, from 3.8.0 through 3.8.6. Users are recommended to upgrade to version 3.8.7 or 3.9.6, which fixes the issue.",
"evidence": "osv:UBUNTU-CVE-2026-84501",
"products": [
{
"name": {
"value": "zookeeper",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.4.5+dfsg-1",
"evidence": "/affected/0/versions"
},
{
"value": "3.4.5+dfsg-1ubuntu0.1~esm1",
"evidence": "/affected/0/versions"
},
{
"value": "3.4.5+dfsg-1ubuntu0.1~esm3",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "zookeeper",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.4.6-8",
"evidence": "/affected/1/versions"
},
{
"value": "3.4.7-1",
"evidence": "/affected/1/versions"
},
{
"value": "3.4.8-1",
"evidence": "/affected/1/versions"
},
{
"value": "3.4.8-1ubuntu0.1~esm1",
"evidence": "/affected/1/versions"
},
{
"value": "3.4.8-1ubuntu0.1~esm2",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "zookeeper",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.4.10-2",
"evidence": "/affected/2/versions"
},
{
"value": "3.4.10-3",
"evidence": "/affected/2/versions"
},
{
"value": "3.4.13-3",
"evidence": "/affected/2/versions"
},
{
"value": "3.4.13-3ubuntu0.1~esm1",
"evidence": "/affected/2/versions"
}
]
},
{
"name": {
"value": "zookeeper",
"evidence": "/affected/3/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.4.13-1",
"evidence": "/affected/3/versions"
},
{
"value": "3.4.13-3",
"evidence": "/affected/3/versions"
},
{
"value": "3.4.13-3build1",
"evidence": "/affected/3/versions"
},
{
"value": "3.4.13-4",
"evidence": "/affected/3/versions"
},
{
"value": "3.4.13-5",
"evidence": "/affected/3/versions"
},
{
"value": "3.4.13-5build1",
"evidence": "/affected/3/versions"
},
{
"value": "3.4.13-5ubuntu0.1",
"evidence": "/affected/3/versions"
}
]
},
{
"name": {
"value": "zookeeper",
"evidence": "/affected/4/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.4.13-5ubuntu4",
"evidence": "/affected/4/versions"
},
{
"value": "3.4.13-6ubuntu2",
"evidence": "/affected/4/versions"
},
{
"value": "3.4.13-6ubuntu3",
"evidence": "/affected/4/versions"
},
{
"value": "3.4.13-6ubuntu4",
"evidence": "/affected/4/versions"
},
{
"value": "3.4.13-6ubuntu4.1",
"evidence": "/affected/4/versions"
}
]
},
{
"name": {
"value": "zookeeper",
"evidence": "/affected/5/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.8.0-11",
"evidence": "/affected/5/versions"
},
{
"value": "3.9.1-1",
"evidence": "/affected/5/versions"
},
{
"value": "3.9.1-1build1",
"evidence": "/affected/5/versions"
},
{
"value": "3.9.1-1build2",
"evidence": "/affected/5/versions"
}
]
},
{
"name": {
"value": "zookeeper",
"evidence": "/affected/6/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.9.5-1",
"evidence": "/affected/6/versions"
},
{
"value": "3.9.5-2",
"evidence": "/affected/6/versions"
}
]
},
{
"name": {
"value": "zookeeper",
"evidence": "/affected/7/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "3.9.3-1build2",
"evidence": "/affected/7/versions"
},
{
"value": "3.9.3-1build3",
"evidence": "/affected/7/versions"
},
{
"value": "3.9.4-1",
"evidence": "/affected/7/versions"
},
{
"value": "3.9.5-1",
"evidence": "/affected/7/versions"
}
]
}
],
"severity": "medium",
"structured": {
"id": "UBUNTU-CVE-2026-84501",
"aliases": [
"UBUNTU-CVE-2026-84501"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N"
},
{
"type": "Ubuntu",
"score": "medium"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "zookeeper",
"purl": "pkg:deb/ubuntu/zookeeper?arch=source&distro=esm-infra-legacy%2Ftrusty",
"ecosystem": "Ubuntu:Pro:14.04:LTS"
},
"versions": [
"3.4.5+dfsg-1",
"3.4.5+dfsg-1ubuntu0.1~esm1",
"3.4.5+dfsg-1ubuntu0.1~esm3"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-84501.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libzookeeper-java",
"binary_version": "3.4.5+dfsg-1ubuntu0.1~esm3"
},
{
"binary_name": "libzookeeper-mt2",
"binary_version": "3.4.5+dfsg-1ubuntu0.1~esm3"
},
{
"binary_name": "libzookeeper-st2",
"binary_version": "3.4.5+dfsg-1ubuntu0.1~esm3"
},
{
"binary_name": "libzookeeper2",
"binary_version": "3.4.5+dfsg-1ubuntu0.1~esm3"
},
{
"binary_name": "python-zookeeper",
"binary_version": "3.4.5+dfsg-1ubuntu0.1~esm3"
},
{
"binary_name": "zookeeper",
"binary_version": "3.4.5+dfsg-1ubuntu0.1~esm3"
},
{
"binary_name": "zookeeper-bin",
"binary_version": "3.4.5+dfsg-1ubuntu0.1~esm3"
},
{
"binary_name": "zookeeperd",
"binary_version": "3.4.5+dfsg-1ubuntu0.1~esm3"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "zookeeper",
"purl": "pkg:deb/ubuntu/zookeeper?arch=source&distro=esm-apps%2Fxenial",
"ecosystem": "Ubuntu:Pro:16.04:LTS"
},
"versions": [
"3.4.6-8",
"3.4.7-1",
"3.4.8-1",
"3.4.8-1ubuntu0.1~esm1",
"3.4.8-1ubuntu0.1~esm2"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-84501.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libzookeeper-java",
"binary_version": "3.4.8-1ubuntu0.1~esm2"
},
{
"binary_name": "libzookeeper-mt2",
"binary_version": "3.4.8-1ubuntu0.1~esm2"
},
{
"binary_name": "libzookeeper-st2",
"binary_version": "3.4.8-1ubuntu0.1~esm2"
},
{
"binary_name": "libzookeeper2",
"binary_version": "3.4.8-1ubuntu0.1~esm2"
},
{
"binary_name": "python-zookeeper",
"binary_version": "3.4.8-1ubuntu0.1~esm2"
},
{
"binary_name": "zookeeper",
"binary_version": "3.4.8-1ubuntu0.1~esm2"
},
{
"binary_name": "zookeeper-bin",
"binary_version": "3.4.8-1ubuntu0.1~esm2"
},
{
"binary_name": "zookeeperd",
"binary_version": "3.4.8-1ubuntu0.1~esm2"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "zookeeper",
"purl": "pkg:deb/ubuntu/zookeeper?arch=source&distro=esm-apps%2Fbionic",
"ecosystem": "Ubuntu:Pro:18.04:LTS"
},
"versions": [
"3.4.10-2",
"3.4.10-3",
"3.4.13-3",
"3.4.13-3ubuntu0.1~esm1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-84501.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libzookeeper-java",
"binary_version": "3.4.13-3ubuntu0.1~esm1"
},
{
"binary_name": "libzookeeper-mt2",
"binary_version": "3.4.13-3ubuntu0.1~esm1"
},
{
"binary_name": "libzookeeper-st2",
"binary_version": "3.4.13-3ubuntu0.1~esm1"
},
{
"binary_name": "python-zookeeper",
"binary_version": "3.4.13-3ubuntu0.1~esm1"
},
{
"binary_name": "zookeeper",
"binary_version": "3.4.13-3ubuntu0.1~esm1"
},
{
"binary_name": "zookeeper-bin",
"binary_version": "3.4.13-3ubuntu0.1~esm1"
},
{
"binary_name": "zookeeperd",
"binary_version": "3.4.13-3ubuntu0.1~esm1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "zookeeper",
"purl": "pkg:deb/ubuntu/zookeeper?arch=source&distro=focal",
"ecosystem": "Ubuntu:20.04:LTS"
},
"versions": [
"3.4.13-1",
"3.4.13-3",
"3.4.13-3build1",
"3.4.13-4",
"3.4.13-5",
"3.4.13-5build1",
"3.4.13-5ubuntu0.1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-84501.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libzookeeper-java",
"binary_version": "3.4.13-5ubuntu0.1"
},
{
"binary_name": "libzookeeper-mt2",
"binary_version": "3.4.13-5ubuntu0.1"
},
{
"binary_name": "libzookeeper-st2",
"binary_version": "3.4.13-5ubuntu0.1"
},
{
"binary_name": "python3-zookeeper",
"binary_version": "3.4.13-5ubuntu0.1"
},
{
"binary_name": "zookeeper",
"binary_version": "3.4.13-5ubuntu0.1"
},
{
"binary_name": "zookeeper-bin",
"binary_version": "3.4.13-5ubuntu0.1"
},
{
"binary_name": "zookeeperd",
"binary_version": "3.4.13-5ubuntu0.1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "zookeeper",
"purl": "pkg:deb/ubuntu/zookeeper?arch=source&distro=jammy",
"ecosystem": "Ubuntu:22.04:LTS"
},
"versions": [
"3.4.13-5ubuntu4",
"3.4.13-6ubuntu2",
"3.4.13-6ubuntu3",
"3.4.13-6ubuntu4",
"3.4.13-6ubuntu4.1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-84501.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libzookeeper-java",
"binary_version": "3.4.13-6ubuntu4.1"
},
{
"binary_name": "libzookeeper-mt2",
"binary_version": "3.4.13-6ubuntu4.1"
},
{
"binary_name": "libzookeeper-st2",
"binary_version": "3.4.13-6ubuntu4.1"
},
{
"binary_name": "python3-zookeeper",
"binary_version": "3.4.13-6ubuntu4.1"
},
{
"binary_name": "zookeeper",
"binary_version": "3.4.13-6ubuntu4.1"
},
{
"binary_name": "zookeeper-bin",
"binary_version": "3.4.13-6ubuntu4.1"
},
{
"binary_name": "zookeeperd",
"binary_version": "3.4.13-6ubuntu4.1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "zookeeper",
"purl": "pkg:deb/ubuntu/zookeeper?arch=source&distro=noble",
"ecosystem": "Ubuntu:24.04:LTS"
},
"versions": [
"3.8.0-11",
"3.9.1-1",
"3.9.1-1build1",
"3.9.1-1build2"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-84501.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libzookeeper-java",
"binary_version": "3.9.1-1build2"
},
{
"binary_name": "libzookeeper-mt2",
"binary_version": "3.9.1-1build2"
},
{
"binary_name": "libzookeeper-st2",
"binary_version": "3.9.1-1build2"
},
{
"binary_name": "python3-zookeeper",
"binary_version": "3.9.1-1build2"
},
{
"binary_name": "zookeeper",
"binary_version": "3.9.1-1build2"
},
{
"binary_name": "zookeeper-bin",
"binary_version": "3.9.1-1build2"
},
{
"binary_name": "zookeeperd",
"binary_version": "3.9.1-1build2"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "zookeeper",
"purl": "pkg:deb/ubuntu/zookeeper?arch=source&distro=stonking",
"ecosystem": "Ubuntu:26.10"
},
"versions": [
"3.9.5-1",
"3.9.5-2"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-84501.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libzookeeper-java",
"binary_version": "3.9.5-2"
},
{
"binary_name": "libzookeeper-mt2",
"binary_version": "3.9.5-2"
},
{
"binary_name": "libzookeeper-st2",
"binary_version": "3.9.5-2"
},
{
"binary_name": "python3-zookeeper",
"binary_version": "3.9.5-2"
},
{
"binary_name": "zookeeper",
"binary_version": "3.9.5-2"
},
{
"binary_name": "zookeeper-bin",
"binary_version": "3.9.5-2"
},
{
"binary_name": "zookeeperd",
"binary_version": "3.9.5-2"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "zookeeper",
"purl": "pkg:deb/ubuntu/zookeeper?arch=source&distro=resolute",
"ecosystem": "Ubuntu:26.04:LTS"
},
"versions": [
"3.9.3-1build2",
"3.9.3-1build3",
"3.9.4-1",
"3.9.5-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-84501.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libzookeeper-java",
"binary_version": "3.9.5-1"
},
{
"binary_name": "libzookeeper-mt2",
"binary_version": "3.9.5-1"
},
{
"binary_name": "libzookeeper-st2",
"binary_version": "3.9.5-1"
},
{
"binary_name": "python3-zookeeper",
"binary_version": "3.9.5-1"
},
{
"binary_name": "zookeeper",
"binary_version": "3.9.5-1"
},
{
"binary_name": "zookeeper-bin",
"binary_version": "3.9.5-1"
},
{
"binary_name": "zookeeperd",
"binary_version": "3.9.5-1"
}
]
}
}
],
"modified": "2026-10-17T13:01:12.735852193Z",
"provider": "osv",
"upstream": [
"CVE-2026-84501"
],
"references": [
"https://ubuntu.com/security/CVE-2026-84501",
"https://www.cve.org/CVERecord?id=CVE-2026-84501"
]
},
"related_cves": [
{
"value": "CVE-2026-84501",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 361250,
"published_at": "2026-09-16T10:16:00+00:00"
}