CVE-2026-34481
Apache Log4J 2.14.0 – 2.25.4
Raw vector
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/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:XSummary
CVE-2026-34481 is a medium-severity Improper Encoding or Escaping of Output (CWE-116) vulnerability in Apache Log4J. Its CVSS base score is 6.3 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Content Injection (T1659); ranked at the 50th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-34481 affects Apache Log4j's JsonTemplateLayout component in versions up to and including 2.25.3. This layout produces invalid JSON output when log events contain non-finite floating-point values such as NaN, Infinity, or -Infinity, which violate RFC 8259 standards. As a result, downstream log processing systems may reject or fail to index the affected log records, leading to potential loss of logging data. The vulnerability is classified under CWE-116 (Improper Encoding or Escaping of Output) with a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N).
Exploitation requires an application that both uses JsonTemplateLayout for logging and logs a MapMessage containing an attacker-controlled floating-point value. An unauthenticated remote attacker meeting these conditions can inject non-finite values, causing the generated JSON to be malformed. This disrupts log ingestion in downstream systems without direct confidentiality or availability impacts, but with high integrity consequences for logging reliability.
Apache advises users to upgrade to Log4j JSON Template Layout version 2.25.4, which resolves the issue by properly handling non-finite floating-point values. Detailed information is available in the official Apache Log4j security advisory at https://logging.apache.org/security.html#CVE-2026-34481, the related GitHub pull request at https://github.com/apache/logging-log4j2/pull/4080, and the mailing list announcement at https://lists.apache.org/thread/n34zdv00gbkdbzt2rx9rf5mqz6lhopcv.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-21412
Vulnerability Data
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…
more
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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.1.2V1.2.1V1.2.3
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Validating that output matches expected content directly mitigates failures to properly encode or escape data for its destination context.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly require proper output encoding to prevent injection and message malformation.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Secure coding standards explicitly require correct output encoding and escaping to preserve message structure.
Security testing can detect missing or incorrect encoding but does not itself implement the control.
Secure development life cycle mandates output encoding/escaping practices that directly prevent improper encoding.
Application security requirements include explicit rules for safe output handling and encoding.
Secure architecture principles reduce the likelihood of missing encoding but do not prescribe the actual technique.