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CVE-2026-34481VulnerabilityPublished Updated

Apache log4j1.2: Apache Log4j's JsonTemplateLayout

Affects apache-log4j1.2Source GCVE Database

0

Mentioned vulnerabilities

Authoritative record:CVE-2026-34481· Medium 6.3

Not known to be exploited · CVSS 6.3 Medium · fixed in 2.25.5 : update apache-log4j1.2 when convenient.

Data as of 26 Oct 2026, 12:55 UTC

CVSS 4.0 base score
6.3Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.6% chance of exploitation in 30 days – higher than 52% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.25.5
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 10 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Affected software

ProductAffectedFixed in
Ubuntu 26.10apache-log4j1.2pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=stonkingOther threatsAffected
  • =1.2.17-11build1
Fixed in–
Ubuntu 26.10apache-log4j2pkg:deb/ubuntu/apache-log4j2?arch=source&distro=stonkingOther threatsAffected
  • =2.19.0-2build1
Fixed in–
Ubuntu 26.04 LTSapache-log4j1.2pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=resoluteOther threatsAffected
  • =1.2.17-11
  • =1.2.17-11build1
Fixed in–
Ubuntu 26.04 LTSapache-log4j2pkg:deb/ubuntu/apache-log4j2?arch=source&distro=resoluteOther threatsAffected
  • =2.19.0-2
  • =2.19.0-2build1
Fixed in–
Ubuntu 25.10apache-log4j1.2pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=questingOther threatsAffected
  • =1.2.17-11
Fixed in–
Ubuntu 25.10apache-log4j2pkg:deb/ubuntu/apache-log4j2?arch=source&distro=questingOther threatsAffected
  • =2.19.0-2
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

Apache Log4j's JsonTemplateLayout https://logging.apache.org/log4j/2.x/manual/json-template-layout.html , in versions up to and including 2.25.3, produces invalid JSON output when log events contain non-finite floating-point values (NaN, Infinity, or -Infinity), which are prohibited by RFC 8259. This may cause downstream log processing systems to reject or fail to index affected records. An attacker can exploit this issue only if both of the following conditions are met: * The application uses JsonTemplateLayout. * The application logs a MapMessage, or logs an object directly (e.g., via Logger.info(Object), which wraps it in an ObjectMessage), where the message contains an attacker-controlled floating-point value. Users are advised to upgrade to Apache Log4j JSON Template Layout 2.25.4, which corrects this issue. Note: The fix released in version 2.25.4 did not cover all affected code paths. CVE-2026-49844 was assigned to the remaining issue, which concerns the MapMessage.asJson() serialization in Apache Log4j API and is fixed in versions 2.25.5 and 2.26.1.

References

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