Apache Log4cxx, Apache Log4cxx (Conan), Apache Log4cxx (Brew): Silent log event loss in XMLLayout due to unescaped XML 1.0 forbidden characters
Summary
| CVE | CVE-2026-40023 |
|---|---|
| State | PUBLISHED |
| Assigner | apache |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-04-10 16:16:32 UTC |
| Updated | 2026-04-10 17:17:12 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 6.3 MEDIUM from [email protected]
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
Problem Types: CWE-116 | CWE-116 CWE-116 Improper Encoding or Escaping of Output
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 6.3 | MEDIUM | 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/C... |
| 4.0 | CNA | CVSS | 6.3 | MEDIUM | 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 |
CVSS v4.0 Breakdown
Attack Vector
NetworkAttack Complexity
HighAttack Requirements
NonePrivileges Required
NoneUser Interaction
NoneConfidentiality
NoneIntegrity
NoneAvailability
NoneSub Conf.
NoneSub Integrity
LowSub Availability
NoneCVSS: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
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Apache Software Foundation | Apache Log4cxx | affected 1.7.0 semver | Not specified |
| CNA | Apache Software Foundation | Apache Log4cxx Conan | affected 1.7.0 semver | Not specified |
| CNA | Apache Software Foundation | Apache Log4cxx Brew | affected 1.7.0 semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| logging.apache.org/log4cxx/1.7.0/classlog4cxx_1_1xml_1_1XMLLayout.html | [email protected] | logging.apache.org | |
| logging.apache.org/cyclonedx/vdr.xml | [email protected] | logging.apache.org | |
| logging.apache.org/security.html | [email protected] | logging.apache.org | |
| lists.apache.org/thread/y15cv3zblg3dfwr5vy6ddbnl4zyrzr8b | [email protected] | lists.apache.org | |
| www.openwall.com/lists/oss-security/2026/04/10/12 | af854a3a-2127-422b-91ae-364da2661108 | www.openwall.com | |
| github.com/apache/logging-log4cxx/pull/609 | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Olawale Titiloye (en)
Additional Advisory Data
| Source | Time | Event |
|---|---|---|
| CNA | 2026-03-15T06:05:00.000Z | Vulnerability reported by Olawale Titiloye |
| CNA | 2026-03-16T06:31:00.000Z | Fix shared publicly by Stephen Webb as pull request #609 |
| CNA | 2026-04-04T03:14:00.000Z | Log4cxx 1.7.0 released |
There are currently no legacy QID mappings associated with this CVE.