Is CVE-2026-40023 in the CISA KEV catalog?

No. CVE-2026-40023 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-40023?

CVE-2026-40023 has a CVSS v3 base score of 5.3 (MEDIUM).

What is the EPSS score for CVE-2026-40023?

CVE-2026-40023 has an EPSS score of 0.50% (39th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-40023?

Upgrade log4cxx to 1.7.0 or later.

CVE & CISA-KEV Catalog

CVE-2026-40023

MEDIUM

5.3

CVSS v3

NVD

Description

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.

CWE-116

How to fix

Remediation Available

log4cxxNVD

Affected:< 1.7.0Fixed in:1.7.0CVE-2026-40023derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityLow

AvailabilityNone

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

Exploit Intelligence

0.50%probability of exploitation in 30 days

39thpercentile

Low risk: more likely to be exploited than 39% of all known CVEs.

References

Patch1

github.com

Vendor Advisory2

Third-Party Advisory1

openwall.com

Product2

Related Vulnerabilities

Other CWE-116 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-38475	Critical	9.1	100%	KEV	Fix
CVE-2022-36446	Critical	9.8	96%	-	Fix
CVE-2021-31806	Medium	6.5	96%	-	Fix
CVE-2022-30781	High	7.5	88%	-	Fix
CVE-2022-36099	Critical	9.9	76%	-	Fix
CVE-2022-36100	Critical	9.9	74%	-	Fix

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Markdown

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HTML

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-21.