UBUNTU-CVE-2026-40021

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Source
https://ubuntu.com/security/CVE-2026-40021
Import Source
https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-40021.json
JSON Data
https://api.osv.dev/v1/vulns/UBUNTU-CVE-2026-40021
Upstream
Published
2026-04-10T16:16:00Z
Modified
2026-05-20T16:25:38Z
Severity
  • 6.3 (Medium) CVSS_V4 - 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 Calculator
  • 5.3 (Medium) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N CVSS Calculator
  • Ubuntu - medium
Summary
[none]
Details

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.

References

Affected packages

Ubuntu:16.04:LTS
log4net

Package

Name
log4net
Purl
pkg:deb/ubuntu/log4net?arch=source&distro=xenial

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

1.*
1.2.10+dfsg-6
1.2.10+dfsg-7
1.2.10+dfsg-7ubuntu0.16.04.1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "liblog4net1.2-cil",
            "binary_version": "1.2.10+dfsg-7ubuntu0.16.04.1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-40021.json"
Ubuntu:18.04:LTS
log4net

Package

Name
log4net
Purl
pkg:deb/ubuntu/log4net?arch=source&distro=bionic

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

1.*
1.2.10+dfsg-7
1.2.10+dfsg-7ubuntu0.18.04.1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "liblog4net1.2-cil",
            "binary_version": "1.2.10+dfsg-7ubuntu0.18.04.1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-40021.json"
Ubuntu:20.04:LTS
log4net

Package

Name
log4net
Purl
pkg:deb/ubuntu/log4net?arch=source&distro=focal

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

1.*
1.2.10+dfsg-7
1.2.10+dfsg-7ubuntu0.20.04.1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "liblog4net1.2-cil",
            "binary_version": "1.2.10+dfsg-7ubuntu0.20.04.1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-40021.json"
Ubuntu:22.04:LTS
log4net

Package

Name
log4net
Purl
pkg:deb/ubuntu/log4net?arch=source&distro=jammy

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

1.*
1.2.10+dfsg-8

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "liblog4net1.2-cil",
            "binary_version": "1.2.10+dfsg-8"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-40021.json"
Ubuntu:24.04:LTS
log4net

Package

Name
log4net
Purl
pkg:deb/ubuntu/log4net?arch=source&distro=noble

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

1.*
1.2.10+dfsg-8
1.2.10+dfsg-9

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "liblog4net1.2-cil",
            "binary_version": "1.2.10+dfsg-9"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-40021.json"
Ubuntu:25.10
log4net

Package

Name
log4net
Purl
pkg:deb/ubuntu/log4net?arch=source&distro=questing

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

1.*
1.2.10+dfsg-9

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "liblog4net1.2-cil",
            "binary_version": "1.2.10+dfsg-9"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-40021.json"
Ubuntu:26.04:LTS
log4net

Package

Name
log4net
Purl
pkg:deb/ubuntu/log4net?arch=source&distro=resolute

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

1.*
1.2.10+dfsg-9
1.2.10+dfsg-9build1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "liblog4net1.2-cil",
            "binary_version": "1.2.10+dfsg-9build1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-40021.json"