How severe is CVE-2026-34478?

No CVSS score has been assigned to CVE-2026-34478 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-34478?

CVE-2026-34478 affects the following packages: org.apache.logging.log4j:log4j-core (Maven), org.apache.logging.log4j:log4j-core (Maven). Ecosystems affected: Maven.

How do I fix CVE-2026-34478?

Update org.apache.logging.log4j:log4j-core to 2.25.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34478 is resolved across your whole dependency graph.

How do I detect CVE-2026-34478 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.logging.log4j:log4j-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-34478 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-34478 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-34478 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-34478?

CVE-2026-34478 has an EPSS (Exploit Prediction Scoring System) score of 1.0%, placing it in the 63th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-34478?

CVE-2026-34478 is classified as CWE-117 (CWE-117), CWE-684 (CWE-684). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-34478 published, and has it been updated?

CVE-2026-34478 was published on April 10, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕ Maven

Not in CISA KEV

CVE-2026-34478 — log4j-core

Fix: apache/logging-log4j2#4074

CVE-2026-34478 is a CWE-117 vulnerability in org.apache.logging.log4j:log4j-core. A fix is available for org.apache.logging.log4j:log4j-core — see the affected versions and patch details below.

Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility

Also known asGHSA-445c-vh5m-36rj

Published

Apr 10, 2026

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

1 / 2

Exploits

None indexed

Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-34478.

EPSS Exploitation Probability

via FIRST.org ↗

1.0%probability of exploitation in next 30 days

Lower Risk+0.02%

Lower risk than most CVEs63th percentile — riskier than 63% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

2 pkgs affected

☕org.apache.logging.log4j:log4j-core☕org.apache.logging.log4j:log4j-core

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

Two distinct issues affect users of stream-based syslog services who configure Rfc5424Layout directly:

The newLineEscape attribute was silently renamed, causing newline escaping to stop working for users of TCP framing (RFC 6587), exposing them to CRLF injection in log output.
The useTlsMessageFormat attribute was silently renamed, causing users of TLS framing (RFC 5425) to be silently downgraded to unframed TCP (RFC 6587), without newline escaping.

Users of the SyslogAppender are not affected, as its configuration attributes were not modified.

Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue.

Affected Packages

2 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.apache.logging.log4j:log4j-core`	≥ 2.21.0&&< 2.25.4	2.25.4`org.apache.logging.log4j:log4j-core:2.25.4`
☕Maven	`org.apache.logging.log4j:log4j-core`	≥ 3.0.0-beta1	No fix

Affected Products

1 product · 4 configurations

Application

log4japache

≥ 2.21.0 && < 2.25.4

1 version

3.0.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.logging.log4j:log4j-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.logging.log4j:log4j-core to 2.25.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34478 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This vulnerability allows log injection via CRLF sequences due to silently renamed security attributes in Rfc5424Layout. This affects Red Hat products that directly configure Rfc5424Layout with stream-based syslog services, potentially enabling an attacker to obscure or manipulate log records. This impact is limited…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-34478 (CC BY 4.0)

Product	Fixed in	Advisory
HawtIO HawtIO 4.4.0	`log4j-core`	RHSA-2026:25089
Red Hat AMQ Broker 7.13.6	`log4j-core`	RHSA-2026:66545
Red Hat AMQ Broker 7.14.1	`log4j-core`	RHSA-2026:66488
Red Hat build of Apache Camel 4.18.1.P1 for Spring Boot 3.5.16	`log4j-core`	RHSA-2026:37390
Red Hat Data Grid 8.6.1	`log4j-core`	RHSA-2026:22619
Streams for Apache Kafka 3.2.1	`log4j-core`	RHSA-2026:54435
Red Hat Offline Knowledge Portal 1.2.13	`offline-knowledge-portal/rhokp-rhel9:1779996999`	RHSA-2026:21773
Red Hat OpenShift AI 2.25	`rhoai/odh-modelmesh-rhel9:1783443816`	RHSA-2026:42644

Frequently Asked Questions

Apache Log4j Core's Rfc5424Layout https://logging.apache.org/log4j/2.x/manual/layouts.html#RFC5424Layout , in versions 2.21.0 through 2.25.3, is vulnerable to log injection via CRLF sequences due to undocumented renames of security-relevant configuration attributes. Two distinct issues affect users of stream-based syslog services who configure Rfc5424Layout directly: * The newLineEscape attribute was silently renamed, causing newline escaping to stop working for users of TCP framing (RFC 6587), exposing them to CRLF injection in log output. * The useTlsMessageFormat attribute was sile

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