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CVE-2026-34478— Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility

Quick assessment

Affected
Apache Software Foundation Apache Log4j Core
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Apache Log4j是美国阿帕奇（Apache）基金会的一款基于Java的开源日志记录工具。 Apache Log4j 2.21.0至2.25.3版本存在安全漏洞，该漏洞源于Rfc5424Layout存在CRLF序列日志注入，可能导致CRLF注入。

AI Predicted 7.5 Difficulty: Easy EPSS 1.19% · P67
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I. Basic Information for CVE-2026-34478

Vulnerability Information
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Vulnerability Title
Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility
Source: CVE Program / CVE List V5
Vulnerability Description
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 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
特定函数功能的不正确供给
Source: CVE Program / CVE List V5
Vulnerability Title
Apache Log4j 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Apache Log4j是美国阿帕奇（Apache）基金会的一款基于Java的开源日志记录工具。 Apache Log4j 2.21.0至2.25.3版本存在安全漏洞，该漏洞源于Rfc5424Layout存在CRLF序列日志注入，可能导致CRLF注入。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Apache Software Foundation Apache Log4j Core 2.21.0 ~ 2.25.4 cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-34478

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III. Intelligence Information for CVE-2026-34478

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Patches & Fixes for CVE-2026-34478 (1)

Mailing List Discussions for CVE-2026-34478 (1)

Same Patch Batch · Apache Software Foundation · 2026-04-10 · 8 CVEs total

CVE-2026-40023 Apache Log4cxx, Apache Log4cxx (Conan), Apache Log4cxx (Brew): Silent log event loss in XM
CVE-2026-40021 Apache Log4net: Silent log event loss in XmlLayout and XmlLayoutSchemaLog4J due to unescap
CVE-2026-34481 Apache Log4j JSON Template Layout: Improper serialization of non-finite floating-point val
CVE-2026-34480 Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden c
CVE-2026-34479 Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescape
CVE-2026-34477 Apache Log4j Core: verifyHostName attribute silently ignored in TLS configuration, allowin
CVE-2026-39304 Apache ActiveMQ Client, Apache ActiveMQ Broker, Apache ActiveMQ All, Apache ActiveMQ: Inco

IV. Related Vulnerabilities

Same product: Apache Log4j Core
Same vendor: Apache Software Foundation
Same weakness: CWE-684

V. Comments for CVE-2026-34478

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