7.5

CVE-2026-34478: apache software foundation apache log4j core Improper Output Neutralization for Logs

CVSS: 7.5v3.1HighAnalyzed
AliasesUBUNTU-CVE-2026-34478CGA-23h9-7f7h-6f9gCGA-25r3-473g-c6gp
Published 10-04-2026Last modified 10-04-2026
Open JSON

Vulnerability summary

CVE-2026-34478 is a high (CVSS 7.5) Improper Output Neutralization for Logs vulnerability in apache software foundation apache log4j core. EPSS estimates a 1.19% chance of exploitation in the next 30 days, higher than 67.3% of scored vulnerabilities.

Overall risk
30/100
0100
Medium · default modelHow is this calculated?
CVSS score
7.5/10
010
High · v3.1 (NVD)
EPSS score
1.19%
0%100%
Low · +0.22 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 0 · Related 1
CGA-QW63-23V7-P6QC

Timeline

  1. 10-04-2026
    PublishedVulnerability first disclosed.
  2. 10-04-2026
    Last modifiedVulnerability information updated.

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.

CVSS metrics

8 scores · 6 sources · 2 versions

EPSS trend

Probability

1.19%

Chance of exploitation in the next 30 days

Percentile

67%

Versus all other CVEs

30-day change

+0.22 pp

From 0.97% on 18-09-2026

18-09-202618-10-2026
EPSS score
1.19%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Chainguard117 products
  • airflow-2All versions (No fix recorded)
  • airflow-3< 3.2.1-r1
  • akhq< 0.27.0-r2
  • apache-activemq-5.19< 5.19.6-r2
  • apache-activemq-6.1< 6.1.8-r3
Wolfi39 products
  • airflow-3< 3.2.1-r1
  • akhq< 0.27.0-r2
  • apache-activemq-artemis< 2.53.0-r5
  • apache-pulsar-4.1All versions (No fix recorded)
  • apache-pulsar-4.2< 4.2.1-r0
Ubuntu2 products
  • apache-log4j1.2All versions (No fix recorded)
  • apache-log4j2All versions (No fix recorded)
Apache1 product
  • log4j≥ 2.21.0, < 2.25.4 | 3.0.0:beta1 | 3.0.0:beta2 | 3.0.0:beta3
Apache software foundation1 product
Org.apache.logging.log4j1 product
  • log4j-core≥ 2.21.0, < 2.25.4 | ≥ 3.0.0-beta1, ≤ 3.0.0-beta3

6 vendors · 161 products

References

12 links
Show all 12 references