CRLF Log Injection in Apache Log4j Core Rfc5424Layout
CVE-2026-34478 is a log injection vulnerability in Apache Log4j Core's Rfc5424Layout affecting versions 2.21.0 through 2.25.3, with supporting context also indicating impact to 3.0.0-beta1 through 3.0.0-beta3. The issue stems from undocumented renaming of security-relevant configuration attributes in Rfc5424Layout. Specifically, the newLineEscape attribute was silently renamed, which can cause newline escaping to stop functioning for deployments using TCP framing under RFC 6587. In a separate but related issue, the useTlsMessageFormat attribute was silently renamed, which can silently downgrade deployments intended to use TLS framing under RFC 5425 to unframed TCP under RFC 6587, also without newline escaping. In affected stream-based syslog deployments that configure Rfc5424Layout directly, attacker-controlled CRLF sequences can therefore be emitted into log output, enabling log injection. Apache stated that SyslogAppender users are not affected because its configuration attributes were not modified.
Are you exposed to this one?
Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.
Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
10 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A vulnerability in Oracle Communications addressed as part of a consolidated fix bundled with CVE-2026-34481.
A high-severity vulnerability affecting HPE Telco Universal SLA Management 4.6 and earlier, associated with potential denial of service and/or CRLF injection impact according to the bulletin.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.