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CVE-2026-49844 medium CVSS 5.9

Vulnerability in org.apache.logging.log4j:log4j-api (CVE-2026-49844)

Summary

Vulnerability in org.apache.logging.log4j:log4j-api (CVE-2026-49844). Data can be tampered with by attackers. Mitigation: upgrade to 2.26.1 or later.

Original description

The description as published by the source.

Improper encoding of non-finite floating-point values during MapMessage JSON serialization in Apache Log4j API produces output that is not valid JSON. This issue affects Apache Log4j API versions 2.13.1 through 2.25.4 and version 2.26.0.

The fix for CVE-2026-34481 did not cover all code paths: when a MapMessage contains a non-finite IEEE 754 value (NaN, Infinity, or -Infinity), MapMessage.asJson() emits the corresponding bare token. RFC 8259 does not permit these tokens, so a conformant parser rejects the resulting document.

The defect is reachable only when both of the following conditions hold:

An attacker who can supply a non-finite value can cause the affected layout to emit malformed JSON, which may corrupt the enclosing log record or disrupt downstream log ingestion and parsing.

Users are advised to upgrade to Apache Log4j API 2.25.5 or 2.26.1, both of which emit RFC 8259-compliant JSON for non-finite values.

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-49844 has been found in org.apache.logging.log4j:log4j-api.
Data can be tampered with by attackers. CVSS score: 5.9/10.
What to do: upgrade org.apache.logging.log4j:log4j-api to 2.26.1 or later.
If unsure, ask your IT team or search "org.apache.logging.log4j:log4j-api CVE-2026-49844" on the vendor's site.

CVE-2026-49844 (org.apache.logging.log4j:log4j-api) — CWE-116 / CVSS v3 5.9
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 2.26.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-116) exists in org.apache.logging.log4j:log4j-api.

📍 Affected scope

Check the vendor advisory for the affected versions of org.apache.logging.log4j:log4j-api.

🔥 Severity

Severity: Medium (CVSS 5.9/10). Data can be tampered with by attackers.

🔧 How to fix

Update to 2.26.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで org.apache.logging.log4j:log4j-api を使っているサービスとバージョンを洗い出す。

  2. 2
    Apply patch patch 
    Upgrade org.apache.logging.log4j:log4j-api to 2.26.1

    ステージング環境で 2.26.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

maven org.apache.logging.log4j:log4j-api
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.26.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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