CVE-2026-49844: Improper encoding of non-finite floating-point values during MapMessage JSON serialization in Apache Log4j API

This month

MEDIUM 5.9REMOTEWATCHLISTUPGRADE

CVE-2026-49844 is a medium-severity flaw (CVSS 5.9) affecting log4j. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 doe

Why this priority

Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 52%)
CISA exploited list	No
Weakness	CWE-116
Published	2026-07-10
Last modified	2026-10-25

Publisher (CNA): Apache Software Foundation · Vendor: apache

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-10 22:16 UTCPublished CVE record published
2026-10-25 15:10 UTCUpdated Record last modified

apache log4j UPGRADE

Affected: >= 2.13.1 and < 2.25.5 · 2.26.0 · 3.0.0 alpha1 · 3.0.0 alpha1_rc1 · 3.0.0 alpha1_rc2 · 3.0.0 beta1 · 3.0.0 beta2

Fixed in: 2.25.5

Safe to downgrade to: a release before 2.13.1

1. Check installed version

apt-cache policy log4j || rpm -q log4j || log4j --version

2. UPGRADE to 2.25.5 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade log4j

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade log4j

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 2.13.1 (Debian / Ubuntu)

apt-cache madison log4j sudo apt install log4j=<VERSION_BEFORE_2.13.1> sudo apt-mark hold log4j

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list log4j sudo dnf downgrade log4j-<VERSION_BEFORE_2.13.1> sudo dnf versionlock add log4j

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-49844?

log4j: upgrade to 2.25.5. Exact commands for each OS are on this page.

Is CVE-2026-49844 being exploited?

CVE-2026-49844 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-49844 affect?

CVE-2026-49844 affects log4j. Severity is medium (CVSS 5.9). 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. T

How urgent is CVE-2026-49844?

Priority 43/100. Remotely exploitable, no login, no user action; On your watchlist

Software pages

Apache Log4j vulnerabilities

References

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