How severe is CVE-2026-34478?

No CVSS score has been assigned to CVE-2026-34478 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-34478?

CVE-2026-34478 affects the following packages: org.apache.logging.log4j:log4j-core (Maven), org.apache.logging.log4j:log4j-core (Maven). Ecosystems affected: Maven.

How do I fix CVE-2026-34478?

Update org.apache.logging.log4j:log4j-core to 2.25.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34478 is resolved across your whole dependency graph.

How do I detect CVE-2026-34478 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.logging.log4j:log4j-core. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2026-34478 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-34478?

O3 pinpoints whether CVE-2026-34478 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2026-34478 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-34478 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was CVE-2026-34478 published, and has it been updated?

CVE-2026-34478 was published on April 10, 2026 and was last updated on July 15, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕ Maven

CVE-2026-34478

CVE-2026-34478 is a security vulnerability in org.apache.logging.log4j:log4j-core. O3 Security confirms whether CVE-2026-34478 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

Apache Log4j Core: Log injection in Rfc5424Layout due to silent configuration incompatibility

Also known asGHSA-445c-vh5m-36rj

Published

Apr 10, 2026

Updated

Jul 15, 2026

Affected

2 pkgs

Patched

1 / 2

Exploits

None indexed

Blast Radius

2 pkgs affected

☕org.apache.logging.log4j:log4j-core☕org.apache.logging.log4j:log4j-core

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

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 Packages

2 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.apache.logging.log4j:log4j-core`	≥ 2.21.0&&< 2.25.4	2.25.4
☕Maven	`org.apache.logging.log4j:log4j-core`	≥ 3.0.0-beta1	No fix

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.logging.log4j:log4j-core. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update org.apache.logging.log4j:log4j-core to 2.25.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34478 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-34478 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-34478. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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 sile

O3 Security · Impact-Aware SCA

Is CVE-2026-34478 in your dependencies?

O3 detects CVE-2026-34478 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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