critical CVSS 9.1

CVE-2026-31886·Docker vulnerability

Dagu is a workflow engine with a built-in Web user interface. Prior to 2.2.4, the dagRunId request field accepted by the inline DAG execution endpoints is passed directly into filepath.Join to construct a temporary directory path without any format validation. Go's filepath.Join resolves .. segments lexically, so a caller can supply a value such as ".." to redirect the computed directory outside the intended /tmp/<name>/<id> path. A deferred cleanup function that calls os.RemoveAll on that directory then runs unconditionally when the HTTP handler returns, deleting whatever directory the traversal resolved to. With dagRunId set to "..", the resolved directory is the system temporary directory (/tmp on Linux). On non-root deployments, os.RemoveAll("/tmp") removes all files in /tmp owned by the dagu process user, disrupting every concurrent dagu run that has live temp files. On root or Docker deployments, the call removes the entire contents of /tmp, causing a system-wide denial of service. This vulnerability is fixed in 2.2.4.

Severity
critical
Software
Docker
Fixed in
2.2.4
Published
2026-03-13

Affected versions

Until: 2.2.4

Fixed in: 2.2.4

How to fix this CVE

Upgrade Docker to version 2.2.4 or later to patch a critical path traversal vulnerability in Dagu's DAG execution endpoints. The vulnerability allows authenticated attackers to manipulate the dagRunId parameter to escape the intended temporary directory and trigger deletion of arbitrary system files, including the entire /tmp directory on Docker deployments. Immediate patching is essential to prevent denial of service and data loss.

sudo dnf update docker-ce

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET /dagu/api/dag/.*/run with dagRunId parameter containing '..\/' or '..\\' or percent-encoded variants (%2e%2e or %252e%252e)

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Block HTTP requests to Dagu DAG execution endpoints where the dagRunId parameter contains directory traversal sequences (../, ..\ or URL-encoded equivalents). Implement strict input validation requiring dagRunId to match the pattern ^[a-zA-Z0-9_-]+$ and reject any requests containing path separators or dot-dot notation.

How to check if you are affected

  1. Check installed Docker version: docker --version or docker version --format='{{.Server.Version}}'
  2. Verify Dagu is running in Docker by checking: docker ps | grep dagu or ps aux | grep dagu
  3. Search application logs for path traversal attempts: grep -r 'dagRunId.*\.\./' /var/log/ or check Dagu logs for requests with '..' in run ID parameters
  4. Confirm patched version is active: docker exec <container_id> dagu version or check the /tmp directory has not been unexpectedly cleared on the host system

FAQ

What is CVE-2026-31886?

CVE-2026-31886 is a critical path traversal vulnerability in Dagu (a workflow engine) where the dagRunId parameter in DAG execution requests is not validated before being used in filepath operations. This allows an authenticated attacker to escape the intended temporary directory and delete arbitrary files on the system.

Is CVE-2026-31886 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available, but the critical severity and ease of exploitation warrant immediate patching.

What versions of Docker are affected by CVE-2026-31886?

All versions of Docker prior to 2.2.4 that bundle or run Dagu as a workflow component are affected. The fix is available in Dagu 2.2.4 and later.

How do I check if my server is vulnerable to CVE-2026-31886?

Run 'docker --version' and verify the version is 2.2.4 or later; check 'docker ps' to identify any containers running Dagu and verify their image tags; examine Dagu application logs for any suspicious dagRunId requests containing '..' or path traversal patterns.

Does Defensia detect CVE-2026-31886?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Docker is installed on a monitored server, CVE-2026-31886 will appear in your dashboard with remediation steps.

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References

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