CVE-2026-344786.9MediumCWE-684

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

Apache Software Foundation · Apache Log4j Core

Vendor fix available · Affected: Apache Software Foundation Apache Log4j Core · Exploitation: unlikely (under 1%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

1.0%probability of exploitation in the next 30 days

63rd percentile

050100

Higher than 63% of scored CVEs

6.9MediumCVSS 4.0

LowMediumHighCrit.

DescriptionCVE.org

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.

Affected products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

Apache Software Foundation · Apache Log4j Corefrom 2.21.0 before 2.25.4; from 3.0.0-beta1 up to and including 3.0.0-beta3

On the Atlas

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Open the Atlas

Exploitation: Unlikely (under 1%). EPSS under 1%, or no score yet.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Incorrect Provision of Specified Functionality · Input Validation and Logic
Vendor: Apache Software Foundation
Published: April 2026
Band: Unlikely (under 1%), April 2026

CoverageNo articles yet

No CyberSIXT article names CVE-2026-34478 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.