Apache Log4j 2.0-alpha1 < 2.25.4 XmlLayout Invalid XML Output (CVE-2026-34480)

medium Nessus Plugin ID 306549

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Synopsis

A logging library installed on the remote host is affected by an improper output encoding vulnerability.

Description

The version of Apache Log4j on the remote host is 2.0-alpha1 through 2.25.3. It is, therefore, affected by a vulnerability:

- The XmlLayout fails to sanitize characters forbidden by the XML 1.0 specification, producing invalid XML output whenever a log message or MDC value contains such characters. Depending on the StAX implementation, this causes either malformed XML or exceptions during logging. (CVE-2026-34480)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Solution

Upgrade to Apache Log4j version 2.25.4 or later.

Plugin Details

Severity: Medium

ID: 306549

File Name: apache_log4j_CVE-2026-34480.nasl

Version: 1.4

Type: Local

Agent: windows, macosx, unix

Family: Misc.

Published: 4/15/2026

Updated: 4/27/2026

Supported Sensors: Frictionless Assessment AWS, Frictionless Assessment Azure, Frictionless Assessment Agent, Nessus Agent, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.4

CVSS v2

Risk Factor: High

Base Score: 7.8

Temporal Score: 5.8

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:C/A:N

CVSS Score Source: CVE-2026-34480

CVSS v3

Risk Factor: High

Base Score: 7.5

Temporal Score: 6.5

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

CVSS v4

Risk Factor: Medium

Base Score: 6.9

Threat Score: 2.7

Threat Vector: CVSS:4.0/E:U

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Vulnerability Information

CPE: cpe:/a:apache:log4j

Required KB Items: installed_sw/Apache Log4j

Exploit Ease: No known exploits are available

Patch Publication Date: 4/10/2026

Vulnerability Publication Date: 4/10/2026

Reference Information

CVE: CVE-2026-34480

IAVA: 2026-A-0324

Detections

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