Skip to main content
No exploitation reportedFix available

CVE-2026-34480

No exploitation reported by the sources we read.

  • Published2026-04-10
  • Fixed in2.25.4
  • WeaknessCWE-116

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2026-04-1016:16CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 15:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-34480?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-34480?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Apache Log4j
BranchAffectedFixed in
2.x≥ 2.0, < 2.25.42.25.4
2.x≥ 2.0-alpha1, < 2.25.42.25.4
3.0= 3.0.0no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • CVE-2026-34480 Red Hat Product Security11 products fixed · 28 known affected

    org.apache.logging.log4j/log4j-core: Apache Log4j Core: Invalid XML output causes denial of service in logging

    redhat-user-workloads/rhaiis-cuda-ubi9-3-2-2 as a component of Red Hat AI Inference Server · redhat-user-workloads/rhaiis-cuda-ubi9-3-3 as a component of Red Hat AI Inference Server · log4j-core as a component of Red Hat build of Apicurio Registry 2 · +25 more

  • RHSA-2026:66545 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat AMQ Broker 7.13.6 release and security update

  • RHSA-2026:66488 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat AMQ Broker 7.14.1 release and security update

  • RHSA-2026:54435 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Streams for Apache Kafka 3.2.1 release and security update

  • RHSA-2026:42644 Red Hat Product Security2 products fixed

    Red Hat Security Advisory: RHOAI 2.25.9 - Red Hat OpenShift AI

  • RHSA-2026:37390 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat Build of Apache Camel 4.18.1.P1 for Spring Boot release.

4 more advisories

Full record on NVD

Fix

  1. Update Apache Log4j to 2.25.4
  2. Vendor fix Red Hat Product Security RHSA-2026:66545 · 1 productBefore applying the update, back up your existing installation, including all applications, configuration files, databases and database settings. The References section of this erratum contains a download link (you must log in to download the update).
  3. Vendor fix Red Hat Product Security RHSA-2026:54435 · 1 productBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
  4. Vendor fix Red Hat Product Security RHSA-2026:42644 · 2 productsFor Red Hat OpenShift AI 2.25.9 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
  5. Vendor fix Red Hat Product Security RHSA-2026:22619 · 1 productBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
  6. Vendor fix Red Hat Product Security RHSA-2026:21773 · 2 productsThe container image provided by this update can be downloaded from the Red Hat container registry at registry.redhat.io using the "podman pull" command.
  7. Workaround from the vendor Red Hat Product Security RHSA-2026:66545 · 1 productMitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CVSS 4.0 vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Published
2026-04-10
Last Modified
2026-06-17
NVD status
Analyzed
MSRC Title
Apache Log4j Core: Silent log event loss in XmlLayout due to unescaped XML 1.0 forbidden characters

Frequently asked questions

What is CVE-2026-34480?

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.

Is CVE-2026-34480 actively exploited?

Active exploitation of CVE-2026-34480 has not been confirmed. Its EPSS score was 1.2% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-34480?

CVE-2026-34480 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

Running Apache Log4j? Hear about its next vulnerability

Surveillance reads the versions in your stack — a domain, a lockfile or a list — checks each CVE against the ranges its sources publish, and alerts you when one you run is exploited or enters CISA KEV. A version it cannot read stays « version not verified ».

Get alerts for this productCISA KEV additions, October 2026Search CVEs

No credit card required · No monthly cap on website lookups · 250 API requests/month

Go further

Related vulnerabilities

Same product first, then the same vendor advisory and the same publication week.

Back to CVE Database