CVE-2026-84501
Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProvider
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProvider
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.
- Record
CVE-2026-84501- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Weakness
- CWE-117
- Updated
- 2026-11-02
EUVDEUVD-2026-80334
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.
- Record
EUVD-2026-80334- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-mm24-r27q-hxg5
An unauthenticated attacker can inject arbitrary fake log lines into Apache ZooKeeper's...
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.
- Record
GHSA-mm24-r27q-hxg5- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Weakness
- CWE-117
- Updated
- 2026-11-02
NVD
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.
- Record
CVE-2026-84501- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Weakness
- CWE-117
- Updated
- 2026-11-02
OSV
Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProvider
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.
- Record
CVE-2026-84501- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Weakness
- CWE-117
- Updated
- 2026-11-02
OSVDEBIAN-CVE-2026-84501
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.
- Record
DEBIAN-CVE-2026-84501- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Updated
- 2026-11-02
OSVUBUNTU-CVE-2026-84501
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.
- Record
UBUNTU-CVE-2026-84501- CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N - Updated
- 2026-11-02
OSVBIT-zookeeper-2026-84501 No score
Apache ZooKeeper: Operational log forgery via newline injection in EnsembleAuthenticationProvider
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.
- Record
BIT-zookeeper-2026-84501- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
zookeeperBitnami |
3.8.0 up to 3.8.7, 3.9.0 up to 3.9.6 | 3.8.73.9.6 |
zookeeperDebian:12 |
All versions, plus listed versions 3.8.0-113.8.0-11+deb12u13.8.0-11+deb12u23.9.1-13.9.2-1 Show 8 moreShow less3.9.2-23.9.3-13.9.3-23.9.4-13.9.4-23.9.5-13.9.5-23.9.6-1 |
None known |
zookeeperDebian:13 |
All versions, plus listed versions 3.9.3-13.9.3-1+deb13u13.9.3-23.9.4-13.9.4-23.9.5-13.9.5-23.9.6-1 |
None known |
zookeeperDebian:14 |
before 3.9.6-1, plus listed versions 3.9.3-13.9.3-23.9.4-13.9.4-23.9.5-13.9.5-2 |
3.9.6-1 |
zookeeperUbuntu:Pro:14.04:LTS |
All versions, plus listed versions 3.4.5+dfsg-13.4.5+dfsg-1ubuntu0.1~esm13.4.5+dfsg-1ubuntu0.1~esm3 |
None known |
zookeeperUbuntu:Pro:16.04:LTS |
All versions, plus listed versions 3.4.6-83.4.7-13.4.8-13.4.8-1ubuntu0.1~esm13.4.8-1ubuntu0.1~esm2 |
None known |
zookeeperUbuntu:Pro:18.04:LTS |
All versions, plus listed versions 3.4.10-23.4.10-33.4.13-33.4.13-3ubuntu0.1~esm1 |
None known |
zookeeperUbuntu:20.04:LTS |
All versions, plus listed versions 3.4.13-13.4.13-33.4.13-3build13.4.13-43.4.13-53.4.13-5build13.4.13-5ubuntu0.1 |
None known |
zookeeperUbuntu:22.04:LTS |
All versions, plus listed versions 3.4.13-5ubuntu43.4.13-6ubuntu23.4.13-6ubuntu33.4.13-6ubuntu43.4.13-6ubuntu4.1 |
None known |
zookeeperUbuntu:24.04:LTS |
All versions, plus listed versions 3.8.0-113.9.1-13.9.1-1build13.9.1-1build2 |
None known |
zookeeperUbuntu:26.10 |
All versions, plus listed versions 3.9.5-13.9.5-2 |
None known |
zookeeperUbuntu:26.04:LTS |
All versions, plus listed versions 3.9.3-1build23.9.3-1build33.9.4-13.9.5-1 |
None known |
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-84501 is a medium vulnerability (CVSS 5.3) in Apache Zookeeper, published September 16, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.74%, the 54th percentile. Fixed in zookeeper 3.8.7.
References
lists.apache.org/thread/ohby1g6zjt72p0w79rhbr41nczzvr33y
openwall.com/lists/oss-security/2026/09/15/7
nvd.nist.gov/vuln/detail/CVE-2026-84501
github.com/advisories/GHSA-mm24-r27q-hxg5
repo.maven.apache.org/maven2
security-tracker.debian.org/tracker/CVE-2026-84501
ubuntu.com/security/CVE-2026-84501
cve.org/CVERecord?id=CVE-2026-84501