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CVE-2026-55841 high CVSS 7.5

Vulnerability in org.graylog2:graylog2-server (CVE-2026-55841)

Summary

Vulnerability in org.graylog2:graylog2-server (CVE-2026-55841). Data can be tampered with by attackers. Mitigation: upgrade to 7.1.2 or later.

Original description

The description as published by the source.

Impact

A security issue has been identified in Graylog affecting the parsing of syslog messages that use a key-value format, such as those generated by Fortigate devices.

The vulnerability allows attackers to overwrite individual message fields, or to produce invalid messages which Graylog will discard. This effectively enables log evasion techniques to obscure malicious activity.

Patches

The issue has been fixed in the following Graylog versions: 6.3.12, 7.0.7, 7.1.2. Users should upgrade to one of these versions or above to remediate the vulnerability.

Graylog Cloud has already been patched.

Workarounds

There are no feasible workarounds for this issue. Upgrading to a patched version is recommended.

To find potentially discarded messages due to parsing errors, customers of Graylog Enterprise or Security can check the Indexing and Processing Failures Index^1.

Credits

Thanks to Jose Luis González, from Fundación Sarenet, with additional analysis by Borja Marcos from Sarenet.

Source: GitHub Security Advisories (Global) 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-2026-55841 has been found in org.graylog2:graylog2-server.
Data can be tampered with by attackers. CVSS score: 7.5/10.
What to do: upgrade org.graylog2:graylog2-server to 7.1.2 or later.
If unsure, ask your IT team or search "org.graylog2:graylog2-server CVE-2026-55841" on the vendor's site.

CVE-2026-55841 (org.graylog2:graylog2-server) — CWE-138 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 7.1.2 — 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-138) exists in org.graylog2:graylog2-server.

📍 Affected scope

Check the vendor advisory for the affected versions of org.graylog2:graylog2-server.

🔥 Severity

Severity: High (CVSS 7.5/10). Data can be tampered with by attackers.

🔧 How to fix

Update to 7.1.2.

🛡️ 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.graylog2:graylog2-server 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.graylog2:graylog2-server to 7.1.2

    ステージング環境で 7.1.2 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.graylog2:graylog2-server
[{"type":"ECOSYSTEM","events":[{"introduced":"7.1.0"},{"fixed":"7.1.2"}]}]

References

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