CVE catalog

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

[CVE catalog]

Severity: Medium · CVSS 5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Published: Sep 16, 2026, 9:28:10 AM UTC
Updated: Sep 16, 2026, 10:16:53 AM UTC
Source: [NVD] · [CVE record]
EPSS: 0.74% · Oct 25, 2026

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.

Vulnerable and fixed packages

Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.

Distribution	Package	Release	Version	Status
Debian	zookeeper	sid	`3.9.6-2`	fixed
Debian	zookeeper	forky	`3.9.6-2`	fixed
Debian	zookeeper	trixie	`3.9.3-1+deb13u1`	vulnerable
Debian	zookeeper	bookworm	`3.8.0-11+deb12u2`	vulnerable
Debian	zookeeper	bookworm-security	`3.8.0-11+deb12u1`	vulnerable
Cpe	zookeeper	Not reported	`3.9.6`	fixed

Fixed-version evidence

Distribution	Package	Type	Release	Fixed version	Urgency	Origin	Bugs
Debian	zookeeper	source	sid	`3.9.6-1`	not yet assigned	Not reported	[1148409]
Debian	zookeeper	source	forky	`3.9.6-1`	not yet assigned	Not reported	[1148409]
Debian	zookeeper	source	trixie	`(unfixed)`	not yet assigned	Not reported	[1148409]
Debian	zookeeper	source	bookworm	`(unfixed)`	not yet assigned	Not reported	[1148409]
Cpe	zookeeper	cpe	Not reported	`3.9.6`	Not reported	NVD-CVE-2026-84501	Not reported

[Debian bug #1148409]

OpenFactory catalog packages

[Debian 12 (Bookworm)]

[libzookeeper-java]Affected
Source package: [zookeeper]
Details (4)
- 3.8.0-11+deb12u2 · all · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · all · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · all · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · all · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
[libzookeeper-java-doc]Affected
Source package: [zookeeper]
Details (4)
- 3.8.0-11+deb12u2 · all · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · all · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · all · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · all · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
[libzookeeper-mt2]Affected
Source package: [zookeeper]
Details (4)
- 3.8.0-11+deb12u2 · amd64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · arm64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · amd64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · arm64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
[libzookeeper-mt-dev]Affected
Source package: [zookeeper]
Details (4)
- 3.8.0-11+deb12u2 · amd64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · arm64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · amd64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · arm64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
[libzookeeper-st2]Affected
Source package: [zookeeper]
Details (4)
- 3.8.0-11+deb12u2 · amd64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · arm64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · amd64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · arm64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
[libzookeeper-st-dev]Affected
Source package: [zookeeper]
Details (4)
- 3.8.0-11+deb12u2 · amd64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · arm64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · amd64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · arm64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
[python3-zookeeper]Affected
Source package: [zookeeper]
Details (4)
- 3.8.0-11+deb12u2 · amd64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · arm64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · amd64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · arm64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
[zookeeper]Affected
Details (4)
- 3.8.0-11+deb12u2 · all · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · all · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · all · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · all · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
[zookeeper-bin]Affected
Source package: [zookeeper]
Details (4)
- 3.8.0-11+deb12u2 · amd64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · arm64 · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · amd64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · arm64 · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
[zookeeperd]Affected
Source package: [zookeeper]
Details (4)
- 3.8.0-11+deb12u2 · all · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u2 · all · bookworm
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · all · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12
- 3.8.0-11+deb12u1 · all · bookworm-security
  Affected
  nvd · zookeeper · debian · bookworm; nvd · zookeeper · debian · 12

[Debian 13 (Trixie)]

[libzookeeper-java]Affected
Source package: [zookeeper]
Details (2)
- 3.9.3-1+deb13u1 · all · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · all · trixie
  Affected
  nvd · zookeeper · debian · 13
[libzookeeper-java-doc]Affected
Source package: [zookeeper]
Details (2)
- 3.9.3-1+deb13u1 · all · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · all · trixie
  Affected
  nvd · zookeeper · debian · 13
[libzookeeper-mt2]Affected
Source package: [zookeeper]
Details (2)
- 3.9.3-1+deb13u1 · amd64 · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · arm64 · trixie
  Affected
  nvd · zookeeper · debian · 13
[libzookeeper-mt-dev]Affected
Source package: [zookeeper]
Details (2)
- 3.9.3-1+deb13u1 · amd64 · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · arm64 · trixie
  Affected
  nvd · zookeeper · debian · 13
[libzookeeper-st2]Affected
Source package: [zookeeper]
Details (2)
- 3.9.3-1+deb13u1 · amd64 · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · arm64 · trixie
  Affected
  nvd · zookeeper · debian · 13
[libzookeeper-st-dev]Affected
Source package: [zookeeper]
Details (2)
- 3.9.3-1+deb13u1 · amd64 · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · arm64 · trixie
  Affected
  nvd · zookeeper · debian · 13
[python3-zookeeper]Affected
Source package: [zookeeper]
Details (2)
- 3.9.3-1+deb13u1 · amd64 · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · arm64 · trixie
  Affected
  nvd · zookeeper · debian · 13
[zookeeper]Affected
Details (2)
- 3.9.3-1+deb13u1 · all · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · all · trixie
  Affected
  nvd · zookeeper · debian · 13
[zookeeper-bin]Affected
Source package: [zookeeper]
Details (2)
- 3.9.3-1+deb13u1 · amd64 · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · arm64 · trixie
  Affected
  nvd · zookeeper · debian · 13
[zookeeperd]Affected
Source package: [zookeeper]
Details (2)
- 3.9.3-1+deb13u1 · all · trixie
  Affected
  nvd · zookeeper · debian · 13
- 3.9.3-1+deb13u1 · all · trixie
  Affected
  nvd · zookeeper · debian · 13

Observed: Oct 23, 2026, 9:09:51 PM UTC

References

[CERT-Bund public advisories] · [Debian Security Tracker] · [FIRST EPSS] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX]