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CVE-2026-34478 is a CRLF log-injection vulnerability in Apache Log4j Core's Rfc5424Layout affecting versions 2.21.0 through 2.25.3. Undocumented renaming of security-relevant configuration attributes affects applications that configure the layout directly for stream-based syslog services. Renaming newLineEscape disables the expected newline escaping for RFC 6587 TCP framing. Renaming useTlsMessageFormat silently changes RFC 5425 TLS message framing to unframed RFC 6587 TCP output without newline escaping. These behaviors expose log output to CRLF injection. SyslogAppender configurations are unaffected because their configuration attributes were not changed. The 3.x prereleases 3.0.0-beta1 through 3.0.0-beta3 are also identified as affected.
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A log-injection vulnerability affecting directly configured Rfc5424Layout instances in Apache Log4j Core 2.21.0–2.25.3. Silent renaming of newLineEscape disables expected newline escaping for TCP syslog framing; renaming of useTlsMessageFormat silently changes TLS framing to unframed TCP without newline escaping. This exposes log output to CRLF injection and undermines log integrity. SyslogAppender users are not affected. The advisory reports CVSS v3 severity of 7.5 and CVSS v4 severity of 6.9. Upgrading to version 2.25.4 or later fixes the issue.
Third-party component vulnerability listed in Dell advisory DSA-2026-393; the affected component and technical impact are not specified.
Third-party component vulnerability listed in Dell's advisory; the content does not provide its component mapping or technical details.
Log injection in Apache Log4j Core via CRLF sequences associated with configuration-attribute renames.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
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