Upstream information

CVE-2026-40021 at MITRE

Description

Apache Log4net's XmlLayout https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list and XmlLayoutSchemaLog4J https://logging.apache.org/log4net/manual/configuration/layouts.html#layout-list , in versions before 3.3.0, fail to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets in MDC property keys and values, as well as the identity field that may carry attacker-influenced data. This causes an exception during serialization and the silent loss of the affected log event.

An attacker who can influence any of these fields can exploit this to suppress individual log records, impairing audit trails and detection of malicious activity.

Users are advised to upgrade to Apache Log4net 3.3.0, which fixes this issue.

SUSE information

Overall state of this security issue: Does not affect SUSE products

This issue is currently rated as having moderate severity.

CVSS v3 Scores
CVSS detail SUSE
Base Score 3.7
Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
Attack Vector Network
Attack Complexity High
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality Impact None
Integrity Impact Low
Availability Impact None
CVSSv3 Version 3.1
CVSS v4 Scores
CVSS detail CNA (Apache Software Foundation) SUSE
Base Score 6.3 6.3
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 CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Attack Vector Network Network
Attack Complexity High High
Attack Requirements None None
Privileges Required None None
User Interaction None None
Vulnerable System Confidentiality Impact None None
Vulnerable System Integrity Impact None Low
Vulnerable System Availability Impact None None
Subsequent System Confidentiality Impact None None
Subsequent System Integrity Impact Low None
Subsequent System Availability Impact None None
CVSSv4 Version 4.0 4.0
SUSE Bugzilla entry: 1261990 [NEW]

No SUSE Security Announcements cross referenced.

SUSE Timeline for this CVE

CVE page created: Fri Apr 10 20:29:44 2026
CVE page last modified: Tue Apr 14 13:57:50 2026