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No exploitation reportedFix available

CVE-2026-40023

No exploitation reported by the sources we read.

  • Published2026-04-10
  • Fixed in1.7.0
  • WeaknessCWE-116

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2026-04-1016:16CVE publishedNVD

Versions per branch

NVD
Apache log4cxx
BranchAffectedFixed in
1.7< 1.7.01.7.0

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA3 products

As apache, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • Apache Software Foundation Apache Log4cxxother versions: not affected
    Affected
    • < 1.7.0fixed in 1.7.0semver
  • Apache Software Foundation Apache Log4cxx (Conan)other versions: not affected

    package log4cxxhttps://conan.io/center

    Affected
    • < 1.7.0fixed in 1.7.0semver
  • Apache Software Foundation Apache Log4cxx (Brew)other versions: not affected

    package log4cxxhttps://brew.sh/

    Affected
    • < 1.7.0fixed in 1.7.0semver

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-04-10

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • log4cxxUbuntu:26.10all versions · no fixed version listed
  • log4cxxUbuntu:26.04:LTSall versions · no fixed version listed
  • log4cxxUbuntu:25.10all versions · no fixed version listed
  • log4cxxUbuntu:24.04:LTSall versions · no fixed version listed
  • log4cxxUbuntu:22.04:LTSall versions · no fixed version listed
  • log4cxxUbuntu:20.04:LTSall versions · no fixed version listed
  • log4cxxUbuntu:18.04:LTSall versions · no fixed version listed
  • log4cxxUbuntu:16.04:LTSall versions · no fixed version listed

6 more package ranges on OSV.dev

Full record on NVD

Fix

  1. Update Apache log4cxx to 1.7.0

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • CISA-ADPSSVC decisionnone2026-04-10
  • CNACVSS 4.06.3known since 2026-10-27
  • NVDCVSS 3.15.3read 2026-10-27
  • CNAweakness (CWE)CWE-116known since 2026-10-27
  • FIRST EPSSEPSS score0.5 %2026-11-08
  • OSVaffected packages—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
CVSS 4.0 vector
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Published
2026-04-10
Last Modified
2026-10-26
NVD status
Analyzed

Frequently asked questions

What is CVE-2026-40023?

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.

Is CVE-2026-40023 actively exploited?

Active exploitation of CVE-2026-40023 has not been confirmed. Its EPSS score was 0.5% on 2026-11-08, the estimated probability of exploitation in the next 30 days.

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

CVE-2026-40023 has a CVSS v3 base score of 5.3 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

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