CVE-2026-84501
No exploitation reported by the sources we read.
- Published2026-09-16
- Fixed in3.9.6 · 3.8.7
- WeaknessCWE-117
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « affected ».With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.
Description
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.
Timeline
dates in UTC- 2026-09-1610:16CVE publishedNVD
Observed activity
isMalicious corpus · updated 2026-10-23 21:37 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-84501?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-84501?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
NVD · OSV| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 3.9 | ≥ 3.9.0, < 3.9.6 | 3.9.6 | NVD · OSV |
| 3.8 | ≥ 3.8.0, < 3.8.7 | 3.8.7 | NVD · OSV |
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Distribution builds and vendor advisories
Packages from OSV.dev and products from the vendors' CSAF advisories.
version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.
Vendor advisories
zookeeper: Apache ZooKeeper: Operational log forgery via newline injection
parent as a component of Red Hat AMQ Broker 7 · zookeeper as a component of Red Hat AMQ Broker 7 · zookeeper-jute as a component of Red Hat AMQ Broker 7 · +17 more
Fix
- Update Apache zookeeper to 3.9.6 · 3.8.7
- Workaround from the vendor Red Hat Product Security CVE-2026-84501 · 20 productsUpdate to Apache ZooKeeper 3.8.7, 3.9.6, or later.
- No fix available, says the vendor Red Hat Product Security CVE-2026-84501 · 10 productsAffected
- No fix planned, says the vendor Red Hat Product Security CVE-2026-84501 · 10 productsWill not fix
Advisories and patches
- lists.apache.orgVendor Advisory
Detection
- Nuclei template
- none so far ProjectDiscovery
- Exploit-DB
- no entry Exploit-DB
- Proof-of-concept repositories
- none listed PoC-in-GitHub
Sources
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- Published
- 2026-09-16
- Last Modified
- 2026-09-18
- NVD status
- Analyzed
Frequently asked questions
What is CVE-2026-84501?
Is CVE-2026-84501 actively exploited?
What is the CVSS score for CVE-2026-84501?
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Related vulnerabilities
Same product first, then the same vendor advisory and the same publication week.