CVE-2026-34478Network attack vector

Log injection via silently ignored framing attributes

Published Apr 10, 2026 · Updated Apr 10, 2026

Log injection in Apache Log4j Core 2.21.0 through 2.25.3 and 3.0.0-beta1 through 3.0.0-beta3 allows attackers to forge syslog records. Rfc5424Layout silently ignores the former newLineEscape and useTlsMessageFormat attributes, disabling CRLF escaping or downgrading TLS framing to unframed TCP. Exploitation requires a stream-based syslog service configured with Rfc5424Layout directly and attacker-controlled logged content; SyslogAppender configurations are unaffected.

CVSS severity7.5
High
EPSS probability0.97%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Log injection in Apache Log4j Core 2.21.0 through 2.25.3 and 3.0.0-beta1 through 3.0.0-beta3 allows attackers to forge syslog records. Rfc5424Layout silently ignores the former newLineEscape and useTlsMessageFormat attributes, disabling CRLF escaping or downgrading TLS framing to unframed TCP. Exploitation requires a stream-based syslog service configured with Rfc5424Layout directly and attacker-controlled logged content; SyslogAppender configurations are unaffected.

The record

CVE
CVE-2026-34478
Published
Apr 10, 2026
Updated
Apr 10, 2026
Vendor
The Apache Software Foundation
Product
Apache Log4j Core
Classifications
CWE-117, CWE-684, T1565.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.21.0 <2.25.4
  2. Affected versionversion=3.0.0-beta1 <=3.0.0-beta3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Log4j Coreversion=2.21.0 <2.25.4; version=3.0.0-beta1 <=3.0.0-beta3

Published CVSS scores

7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
6.9Apache Software FoundationCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-117Improper Output Neutralization for Logs
CWE-684Incorrect Provision of Specified Functionality
T1565.001Stored Data Manipulation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo