TI-2026-28866 Aliases CVE-2026-40023 GHSA-q8qr-wp2r-738r

Improper output encoding in Apache Log4cxx

LOW 29CWE-116Published 2026-04-10 · Updated 2026-04-10

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: High
Attack requirements: None
Impact type: —
Confidentiality · integrity · availability: None · None · None
Fix status: Partial Red Hat: 1 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat.

Summary

Apache Log4cxx's XMLLayout https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html , in versions before 1.7.0, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets in log messages, NDC, and MDC property keys and values, producing invalid XML output. Conforming XML parsers must reject such documents with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records. An attacker who can influence logged data can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity. Users are advised to upgrade to Apache Log4cxx 1.7.0, which fixes this issue.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00518 44th percentileScored 2026-11-07

Fix Partial Apache Log4cxx (Apache Software Foundation): 1.7.0Apache Log4cxx (Conan) (Apache Software Foundation): 1.7.0+1 more productRed Hat: 1 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
Apache	Apache Log4cxx	before 1.7.0	1.7.0	Patch available	CNA
Apache	Apache Log4cxx (Conan)	before 1.7.0	1.7.0	Patch available	CNA
Apache	Apache Log4cxx (Brew)	before 1.7.0	1.7.0	Patch available	CNA

Apache Log4cxx VendorApache Affected before 1.7.0 Fixed in 1.7.0 Patch available CNA
Apache Log4cxx (Conan) VendorApache Affected before 1.7.0 Fixed in 1.7.0 Patch available CNA
Apache Log4cxx (Brew) VendorApache Affected before 1.7.0 Fixed in 1.7.0 Patch available CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:apache:log4cxx::::::::	before 1.7.0	Vulnerable	Apache

cpe:2.3:a:apache:log4cxx:*:*:*:*:*:*:*:* Versions before 1.7.0 Vulnerable ·Apache

Remediation

Fix · CNA Apache Log4cxx (Apache Software Foundation) Fixed in 1.7.0
Fix · CNA Apache Log4cxx (Conan) (Apache Software Foundation) Fixed in 1.7.0
Fix · CNA Apache Log4cxx (Brew) (Apache Software Foundation) Fixed in 1.7.0

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Red Hat Enterprise Linux 7	Affected	No fix planned: Out of support scope

Timeline

2026-10-02 Threatist record created from CVE-2026-40023
2026-10-03 Alias added: GHSA-q8qr-wp2r-738r
2026-10-25 EPSS moved to the below the 50th percentile

References

Patch 1

https://github.com/apache/logging-log4cxx/pull/609

Advisory 4

Other 1

https://logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html

TI-2023-14775 Apache Log4cxx: SQL injection when using ODBC appender CVSS 3.1HIGH 8.8
TI-2025-34567 Apache Log4cxx: Improper escaping with JSONLayout CVSS 4.0MEDIUM 6.3
TI-2025-34566 Apache Log4cxx: Improper HTML escaping in HTMLLayout CVSS 4.0LOW 2.1

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences