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Apache Log4j 2.13.1 < 2.25.5 / 2.26.0 < 2.26.1 Improper JSON Serialization (CVE-2026-49844)

medium Nessus Plugin ID 327598

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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 affected by a vulnerability:

 - Improper encoding of non-finite floating-point values during MapMessage JSON serialization in Apache Log4j API produces output that is not valid JSON. When a MapMessage contains a non-finite IEEE 754 value (NaN, Infinity, or -Infinity), MapMessage.asJson() emits the corresponding bare token. RFC 8259 does not permit these tokens, so a conformant parser rejects the resulting document. An attacker who can supply a non-finite value can cause the affected layout to emit malformed JSON, which may corrupt the enclosing log record or disrupt downstream log ingestion and parsing. (CVE-2026-49844)

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 2.25.5 or 2.26.1 or later. For other branches, upgrade to a fixed version when available.

See Also

https://logging.apache.org/security.html#CVE-2026-49844

Plugin Details

Severity: Medium

ID: 327598

File Name: apache_log4j_CVE-2026-49844.nasl

Version: 1.3

Type: Local

Agent: windows, macosx, unix

Family: Misc.

Published: 7/17/2026

Updated: 7/20/2026

Supported Sensors: Frictionless Assessment Agent, Frictionless Assessment AWS, Frictionless Assessment Azure, Nessus Agent, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Low

Score: 3

Percentile: 23.72

CVSS v2

Risk Factor: Medium

Base Score: 5.4

Temporal Score: 4

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

CVSS Score Source: CVE-2026-49844

CVSS v3

Risk Factor: Medium

Base Score: 5.9

Temporal Score: 5.2

Vector: CVSS:3.0/AV:N/AC:H/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: 6.3

Threat Score: 1.7

Threat Vector: CVSS:4.0/E:U

Vector: CVSS:4.0/AV:N/AC:L/AT:P/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: 7/10/2026

Vulnerability Publication Date: 7/10/2026

Reference Information

CVE: CVE-2026-49844

IAVA: 2026-A-0688