CVE-2026-34479Network attack vector

Log record suppression via invalid XML output

Published Apr 10, 2026 · Updated Apr 10, 2026

Improper XML output encoding in Apache Log4j 1.2 Bridge allows remote attackers to suppress downstream log records through crafted logged data. Transform.escapeHtmlTags and Transform.appendEscapingCData escape markup without replacing XML 1.0-forbidden code points, so Log4j1XmlLayout emits malformed XML that conforming parsers reject. Exposure requires Log4j1XmlLayout in a Log4j Core 2 configuration or org.apache.log4j.xml.XMLLayout through the compatibility layer, and only affected records can be dropped or left unindexed.

CVSS severity6.9
Medium
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper XML output encoding in Apache Log4j 1.2 Bridge allows remote attackers to suppress downstream log records through crafted logged data. Transform.escapeHtmlTags and Transform.appendEscapingCData escape markup without replacing XML 1.0-forbidden code points, so Log4j1XmlLayout emits malformed XML that conforming parsers reject. Exposure requires Log4j1XmlLayout in a Log4j Core 2 configuration or org.apache.log4j.xml.XMLLayout through the compatibility layer, and only affected records can be dropped or left unindexed.

The record

CVE
CVE-2026-34479
Published
Apr 10, 2026
Updated
Apr 10, 2026
Vendor
The Apache Software Foundation
Product
Apache Log4j 1.2 Bridge
Classifications
CWE-116, T1070
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.7 <2.25.4
  2. Affected versionversion=3.0.0-alpha1 <=3.0.0-beta2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Log4j 1.2 Bridgeversion=2.7 <2.25.4; version=3.0.0-alpha1 <=3.0.0-beta2

Published CVSS scores

6.9Apache Software FoundationCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-116Improper Encoding or Escaping of Output
T1070Indicator Removal

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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