CVE-2026-49844
Apache Log4j API: Improper serialization of non-finite floating-point values in MapMessage.asJson()
Description
Improper encoding of non-finite floating-point values during MapMessage JSON serialization in Apache Log4j API produces output that is not valid JSON. This issue affects Apache Log4j API versions 2.13.1 through 2.25.4 and version 2.26.0. The fix for CVE-2026-34481 did not cover all code paths: 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. The defect is reachable only when both of the following conditions hold: * The application uses the message resolver https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-message of JsonTemplateLayout or any other layout that relies on MapMessage.asJson() or MapMessage.getFormattedMessage(new String[]{"JSON"}). * The application logs a MapMessage that contains an attacker-controlled floating-point value. 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. Users are advised to upgrade to Apache Log4j API 2.25.5 or 2.26.1, both of which emit RFC 8259-compliant JSON for non-finite values.
INFO
Published Date :
July 10, 2026, 10:16 p.m.
Last Modified :
July 14, 2026, 8:03 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 4.0 | MEDIUM | f0158376-9dc2-43b6-827c-5f631a4d8d09 | ||||
| CVSS 4.0 | MEDIUM | [email protected] |
Solution
- Upgrade Apache Log4j API to 2.25.5 or 2.26.1.
- Ensure application uses JsonTemplateLayout or similar layouts.
- Validate logging of MapMessages with floating-point values.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-49844.
| URL | Resource |
|---|---|
| https://github.com/apache/logging-log4j2/pull/4163 | Issue Tracking Patch |
| https://logging.apache.org/cyclonedx/vdr.xml | Vendor Advisory |
| https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-message | Product |
| https://logging.apache.org/security.html#CVE-2026-49844 | Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-49844 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-49844
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-49844 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-49844 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Jul. 14, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N Added CPE Configuration OR *cpe:2.3:a:apache:log4j:3.0.0:alpha1:*:*:*:*:*:* *cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc1:*:*:*:*:*:* *cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc2:*:*:*:*:*:* *cpe:2.3:a:apache:log4j:3.0.0:beta1:*:*:*:*:*:* *cpe:2.3:a:apache:log4j:3.0.0:beta2:*:*:*:*:*:* *cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:* versions from (including) 2.13.1 up to (excluding) 2.25.5 *cpe:2.3:a:apache:log4j:2.26.0:*:*:*:*:*:*:* Added Reference Type Apache Software Foundation: https://github.com/apache/logging-log4j2/pull/4163 Types: Issue Tracking, Patch Added Reference Type Apache Software Foundation: https://logging.apache.org/cyclonedx/vdr.xml Types: Vendor Advisory Added Reference Type Apache Software Foundation: https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-message Types: Product Added Reference Type Apache Software Foundation: https://logging.apache.org/security.html#CVE-2026-49844 Types: Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 14, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-49844', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-14T13:56:31.652710Z'} -
New CVE Received by [email protected]
Jul. 10, 2026
Action Type Old Value New Value Added Affected [{'cpes': ['cpe:2.3:a:apache:log4j_api:*:*:*:*:*:*:*:*'], 'vendor': 'Apache Software Foundation', 'product': 'Apache Log4j API', 'versions': [{'status': 'affected', 'version': '2.13.1', 'lessThan': '2.25.5', 'versionType': 'maven'}, {'status': 'affected', 'version': '2.26.0', 'lessThan': '2.26.1', 'versionType': 'maven'}, {'status': 'affected', 'version': '3.0.0-alpha1', 'versionType': 'maven', 'lessThanOrEqual': '3.0.0-beta2'}], 'packageURL': 'pkg:maven/org.apache.logging.log4j/log4j-api', 'packageName': 'org.apache.logging.log4j:log4j-api', 'collectionURL': 'https://repo.maven.apache.org/maven2', 'defaultStatus': 'unaffected'}] Added Description Improper encoding of non-finite floating-point values during MapMessage JSON serialization in Apache Log4j API produces output that is not valid JSON. This issue affects Apache Log4j API versions 2.13.1 through 2.25.4 and version 2.26.0. The fix for CVE-2026-34481 did not cover all code paths: 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. The defect is reachable only when both of the following conditions hold: * The application uses the message resolver https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-message of JsonTemplateLayout or any other layout that relies on MapMessage.asJson() or MapMessage.getFormattedMessage(new String[]{"JSON"}). * The application logs a MapMessage that contains an attacker-controlled floating-point value. 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. Users are advised to upgrade to Apache Log4j API 2.25.5 or 2.26.1, both of which emit RFC 8259-compliant JSON for non-finite values. Added CVSS V4.0 AV:N/AC:L/AT:P/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 Added CWE CWE-116 Added Reference https://github.com/apache/logging-log4j2/pull/4163 Added Reference https://logging.apache.org/cyclonedx/vdr.xml Added Reference https://logging.apache.org/log4j/2.x/manual/json-template-layout.html#event-template-resolver-message Added Reference https://logging.apache.org/security.html#CVE-2026-49844