7.5

CVE-2026-34480: apache software foundation apache log4j core Improper Encoding or Escaping of Output

CVSS: 7.5v3.1HighAnalyzed
AliasesUBUNTU-CVE-2026-34480DEBIAN-CVE-2026-34480CGA-2845-7j77-24h6
Published 10-04-2026Last modified 10-04-2026
Open JSON

Vulnerability summary

CVE-2026-34480 is a high (CVSS 7.5) Improper Encoding or Escaping of Output 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 1 · Related 2
OPENSUSE-SU-2026:10544-1CGA-WQHW-VH22-JWGM

Timeline

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

Description

Apache Log4j Core's XmlLayout https://logging.apache.org/log4j/2.x/manual/layouts.html#XmlLayout , in versions up to and including 2.25.3, fails to sanitize characters forbidden by the XML 1.0 specification https://www.w3.org/TR/xml/#charsets producing invalid XML output whenever a log message or MDC value contains such characters. The impact depends on the StAX implementation in use: * JRE built-in StAX: Forbidden characters are silently written to the output, producing malformed XML. Conforming parsers must reject such documents with a fatal error, which may cause downstream log-processing systems to drop the affected records. * Alternative StAX implementations (e.g., Woodstox https://github.com/FasterXML/woodstox , a transitive dependency of the Jackson XML Dataformat module): An exception is thrown during the logging call, and the log event is never delivered to its intended appender, only to Log4j's internal status logger. Users are advised to upgrade to Apache Log4j Core 2.25.4, which corrects this issue by sanitizing forbidden characters before XML output.

CVSS metrics

9 scores · 7 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

Chainguard172 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
Wolfi26 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
Apache1 product
  • log4j≥ 2.0, < 2.25.4 | 3.0.0:alpha1 | 3.0.0:alpha1_rc1 | 3.0.0:alpha1_rc2 | 3.0.0:beta1 | 3.0.0:beta2 | 3.0.0:beta3
Apache software foundation1 product

4 vendors · 200 products · Showing 200 of 225. Use Open JSON for the complete list.

References

13 links
Show all 13 references