> CVE-2026-40021 [MEDIUM]

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PUBLISHED
2026-04-10 16:16
MODIFIED
2026-04-10 16:16
CVSS_SCORE V3
6.3
EPSS (Prob. Exploit)
0.80%
Top 43.1%
DATA SOURCES:
NVD đź”— 2026-04-10 CWE MITRE đź”— 2026-11-01 FIRST EPSS đź”— 2026-11-08 GITHUB đź”— 2026-10-28 OSV đź”— 2026-11-02

> 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.

> AFFECTED_PRODUCTS

ℹ️ Aucun produit affecté n'a encore été publié par NVD pour cette CVE.

> CVSS V3 METRICS

CVSS_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

> MÉTRIQUES CVSS DÉTAILLÉES

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
Métrique Valeur Interprétation
AV (Vecteur d'Attaque)
Attack Vector
Network (N)
Exploit possible à distance via réseau (HTTP, API, etc.)
AC (Complexité d'Attaque)
Attack Complexity
High (H)
Conditions spécifiques doivent être réunies pour exploiter
PR (Privilèges Requis)
Privileges Required
None (N)
Aucune authentification requise
UI (Interaction Utilisateur)
User Interaction
None (N)
Aucune interaction utilisateur nécessaire
S (Périmètre)
Scope
Unchanged (U)
Impact reste dans le périmètre du composant compromis
C (Impact Confidentialité)
Confidentiality Impact
None (N)
Aucune divulgation d'informations
I (Impact Intégrité)
Integrity Impact
None (N)
Aucune modification de données possible
A (Impact Disponibilité)
Availability Impact
None (N)
Aucune interruption de service

> RÉSUMÉ DES IMPACTS

Confidentialité
None
Aucune divulgation d'informations
Intégrité
None
Aucune modification de données possible
Disponibilité
None
Aucune interruption de service

> WEAKNESSES

CWE-116

> CWE DETAILED DESCRIPTIONS

CWE-116: Improper Encoding or Escaping of Output - The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

> GITHUB SECURITY ADVISORY

GHSA-4f7c-pmjv-c25w MODERATE

Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescaped XML 1.0 forbidden characters

AFFECTED PACKAGES:
NUGET / log4net
< 3.3.0
Fixed in: 3.3.0

> OSV (GOOGLE OPEN SOURCE VULNERABILITIES)

Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescaped XML 1.0 forbidden characters

AFFECTED PACKAGES:
Unknown / Unknown
27 versions affected
ALIASES:
GHSA-4f7c-pmjv-c25w

> HISTORIQUE DES MODIFICATIONS

Première apparition
10/04/2026 16:16
Source: NVD
📊 ENRICHISSEMENT 01/05/2026 06:01
CWE
Champ modifié: Description CWE
Ancienne valeur:
N/A
Nouvelle valeur:
CWE-116: Improper Encoding or Escaping of Output - The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done in...
Total des modifications: 1 Dernière mise à jour: 6 months ago

> REFERENCES

https://github.com/apache/logging-log4net/pull/280
https://lists.apache.org/thread/q8otftjswhk69n3kxslqg7cobr0x4st7
https://logging.apache.org/cyclonedx/vdr.xml
https://logging.apache.org/log4net/manual/configuration/layouts.html
https://logging.apache.org/security.html#CVE-2026-40021
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