OS Command Injection in linuxfabrik-lib (CVE-2026-55426)
Summary
OS command injection in linuxfabrik-lib (CVE-2026-55426). Successful exploitation can lead to full system takeover. Exploitable via shell_exec. Mitigation: upgrade to 5.0.0 or later.
Original description
The description as published by the source.
Summary
When a check plugin places user provided input inside a command which is passed to shell_exec, an attacker can abuse this to run arbitrary commands. This is mainly dangerous for plugins which are listed in the sudoers file, because this allows an attacker controlling the nagios user to get root privileges.
Details
An example for this is the restic-check plugin, where the --repo argument is placed inside the command argument of shell_exec. As an example, an attacker could use the --repo argument |touch /root/nagios-was-here|. The full restic command is assembled to the string restic --json --repo=|touch /root/nagios-was-here| --password-file= check before it is passed to shell_exec. shell_exec then splits the command up in three parts at the | boundaries and executes the parts separately, which also executes the embedded command touch /root/nagios-was-here.
PoC
This PoC shows how the nagios user can use this to create a file inside /root.
nagios@test-vm:/$ sudo /usr/lib64/nagios/plugins/restic-check --repo '|touch /root/nagios-was-here|'
Impact
The vulnerability is a local privilege escalation.
Fix
Switch from | to an array
Remove the | split functionality. Instead, modify shell_exec to accept either a string or an array of strings. If an array is provided, the commands are chained together like they currently are when using |. If a string is provided, no split should be performed. You could also introduce a s…
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-2026-55426 has been found in linuxfabrik-lib.
Attackers can target a specific entry point like shell_exec over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 7.8/10.
What to do: upgrade linuxfabrik-lib to 5.0.0 or later.
If unsure, ask your IT team or search "linuxfabrik-lib CVE-2026-55426" on the vendor's site.
CVE-2026-55426 (linuxfabrik-lib) — CWE-78 / CVSS v3 7.8
Attack vector: local / no user interaction
Attack surface: shell_exec / shlex.quote / Popen / shell_exec_with_user_input
Patched: 5.0.0 — 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.
OS command injection (CWE-78) exists in linuxfabrik-lib. Attackers reach the vulnerable code path via shell_exec.
Check the vendor advisory for the affected versions of linuxfabrik-lib. Attack surface: shell_exec / shlex.quote / Popen / shell_exec_with_user_input.
Severity: High (CVSS 7.8/10). Successful exploitation can lead to full system takeover.
Update to 5.0.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'linuxfabrik-lib' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'linuxfabrik-lib' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
linuxfabrik-libを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade linuxfabrik-lib to 5.0.0ステージング環境で 5.0.0 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。
-
3Post-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。