Apache log4j1.2: Apache Log4j's JsonTemplateLayout
Affects apache-log4j1.2Source GCVE Database
Mentioned vulnerabilities
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
- 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:NExploitation evidence
Disclosed: evidence found.
CVE published 10 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.10apache-log4j1.2pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.10apache-log4j2pkg:deb/ubuntu/apache-log4j2?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSapache-log4j1.2pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSapache-log4j2pkg:deb/ubuntu/apache-log4j2?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 25.10apache-log4j1.2pkg:deb/ubuntu/apache-log4j1.2?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10apache-log4j2pkg:deb/ubuntu/apache-log4j2?arch=source&distro=questingOther threats | Affected
| 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
- ubuntu.com/security/CVE-2026-34481 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-34481 (opens in a new tab)
- lists.apache.org/thread/n34zdv00gbkdbzt2rx9rf5mqz6lhopcv (opens in a new tab)
- logging.apache.org/security.html (opens in a new tab)
- github.com/apache/logging-log4j2/pull/4080 (opens in a new tab)
- logging.apache.org/cyclonedx/vdr.xml (opens in a new tab)
- logging.apache.org/log4j/2.x/manual/json-template-layout.html (opens in a new tab)
- openwall.com/lists/oss-security/2026/04/10/10 (opens in a new tab)