CVE-2026-34479

HIGHNVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 7.5 under NVD CVSS v3. EPSS exploit probability: 0.1%, top 68% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
7.5
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 7.5Exploit: NoneExposed: 0

A fix is available — apply it.

The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records.

Two groups of users are affected:

* Those using Log4j1XmlLayout directly in a Log4j Core 2 configuration file. * Those using the Log4j 1 configuration compatibility layer with org.apache.log4j.xml.XMLLayout specified as the layout class.

Users are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue.

Note: The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the Log4j 1 to Log4j 2 migration guide https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html , and specifically the section on eliminating reliance on the bridge.

CVSS v3
7.5
EG Score
7.5(medium)
EPSS
41.5%
KEV
Not listed

Published

April 10, 2026

Last Modified

May 6, 2026

Advisory Details (6)

Auto-updated May 6, 2026
No patch confirmed yet.
generic

oss-security - CVE-2026-34479: Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters

http://www.openwall.com/lists/oss-security/2026/04/10/8
generic

Security :: Apache Logging Services

https://logging.apache.org/security.html#CVE-2026-34479
generic

Migrating from Log4j 1 :: Apache Log4j

https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html
generic
https://logging.apache.org/cyclonedx/vdr.xml
generic
https://lists.apache.org/thread/gd0hp6mj17rn3kj279vgy4p7kd4zz5on
generic

Log4j1XmlLayout: replace invalid XML characters with U+FFFD by ppkarwasz · Pull Request #4078 · apache/logging-log4j2 · GitHub

https://github.com/apache/logging-log4j2/pull/4078

Vendor Advisories for CVE-2026-34479(2)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatoffline-knowledge-portal/rhokp-rhel9:17799969992026-05-28redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
Maven(1)
PackageVulnerable rangeFixed inDependents
org.apache.logging.log4j:log4j-1.2-api3.0.0-beta1, 3.0.0-beta2——

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 9× in last 7d / 42× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 107 total refreshes for this CVE.

  1. 2026-07-15 16:57 UTCEPSS rescore
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  20. 2026-06-15 04:23 UTCVendor advisory
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Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2026-34479?
CVE-2026-34479 is a high vulnerability published on April 10, 2026. The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log…
When was CVE-2026-34479 disclosed?
CVE-2026-34479 was first published in the National Vulnerability Database on April 10, 2026, with the most recent update on May 6, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-34479 actively exploited?
CVE-2026-34479 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 41.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-34479?
CVE-2026-34479 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-34479?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-34479, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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