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CVE-2026-84501

MEDIUM 5.3 ALL-YEARS

Published 2026-09-16 · Last modified 2026-09-16 · apache · NVD: Analyzed

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.

LIMITED SIGNALS

No known exploitation, public exploit, or elevated probability at this time. Track for changes.

Exploitation likelihood

0.7%chance of exploitation in 30 days · 54th percentile

○ In CISA KEV○ Public exploit / PoC◆ SSVC: exploitation none, automatable yes

Impact if exploited

5.3CVSS 3.1 · MEDIUM · ADP

  • ConfidentialityNone
  • IntegrityLow
  • AvailabilityNone

What an attacker needs

  • ✓Access: Reachable over the network — no local access needed
  • ✓Privileges: No account or privileges required
  • ✓User interaction: No user interaction needed
  • ✓Complexity: No special conditions — reliably repeatable

✓ lowers the bar for an attacker · ⚠ raises it

Proof of concept & exploit code

No public exploit or proof-of-concept code is catalogued for this CVE (no ExploitDB, Nuclei, or CISA-KEV entry). It may still exist — search GitHub or check the references below.

Affected

Vendors Apache Software Foundation Apache

Products Apache Zookeeper Zookeeper

Weakness (CWE)

  • CWE-117: Improper output neutralization for logs

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Known Affected Software Configurations

VendorProductVersion range
ApacheZookeeper≥ 3.8.0 and < 3.8.7
ApacheZookeeper≥ 3.9.0 and < 3.9.6

All CVSS metrics

  • MEDIUM 5.3 v3.1 · ADP Primary
    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
  • MEDIUM 5.3 v3.1 · NVD Secondary
    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

References

Advisories

Technical & other

Sources: NVD · CVE.org · EPSS