CVE-2026-31976 — xygeni/xygeni-action
CVE-2026-31976 is a CWE-506 vulnerability in xygeni/xygeni-action. A fix is available for xygeni/xygeni-action — see the affected versions and patch details below.
xygeni-action v5 tag poisoned with C2 backdoor
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-31976.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
xygeni/xygeni-actionReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects GitHub Actions packages — download data is not available via public APIs for these ecosystems.
Description
Description
On March 3, 2026, an attacker with access to compromised credentials created a series of pull requests (#46, #47, #48) injecting obfuscated shell code into action.yml. The PRs were blocked by branch protection rules and never merged into the main branch.
However, the attacker used the compromised GitHub App credentials to move the mutable v5 tag to point at the malicious commit (4bf1d4e19ad81a3e8d4063755ae0f482dd3baf12) from one of the unmerged PRs. This commit remained in the repository's git object store, and any workflow referencing @v5 would fetch and execute it.
The malicious code, disguised as a "scanner version telemetry" step, operates as follows:
- Registers the CI runner with a C2 server at
91.214.78.178(viasecurity-verify.91.214.78.178.nip.io), transmitting hostname, username, and OS version. - Polls the C2 server every 2–7 seconds for 180 seconds, receiving and executing arbitrary shell commands via
eval. - Compresses and base64-encodes command output before exfiltrating it back to the C2 server.
The implant runs silently in the background alongside the legitimate scan, suppresses all errors, skips TLS certificate verification, and uses randomized polling intervals to evade detection.
Impact
This is a supply chain compromise via tag poisoning. Any GitHub Actions workflow referencing xygeni/xygeni-action@v5 during the affected window (approximately March 3–10, 2026) executed a C2 implant that granted the attacker arbitrary command execution on the CI runner for up to 180 seconds per workflow run.
The severity is set to Critical based on the potential impact. However, several factors reduce the realized risk: the v5 tag was primarily referenced by Xygeni-owned and Xygeni-affiliated repositories; no external public repositories were found using the compromised tag (though usage in private repositories cannot be ruled out); the exposure window was approximately 6 days; and no confirmed exploitation of downstream users has been established to date.
Patches
The compromised v5 tag has been removed from the repository. Users should update their workflows to pin to the verified safe commit SHA corresponding to v6.4.0:
uses: xygeni/xygeni-action@13c6ed2797df7d85749864e2cbcf09c893f43b23 # v6.4.0
Workflows still referencing @v5 will fail with a reference not found error, as the tag no longer exists.
If your workflows ran with @v5 during the affected window, you should also:
- Rotate all secrets that were available to the CI runner (repository secrets, environment secrets, deploy keys, cloud provider tokens).
- Audit CI logs for outbound connections to
91.214.78.178or DNS lookups forsecurity-verify.91.214.78.178.nip.io. - Review recent releases and published artifacts for signs of tampering.
Workarounds
As an alternative to using the GitHub Action, you may install and run the Xygeni scanner directly via the CLI installation method documented at https://docs.xygeni.io/xygeni-scanner-cli/xygeni-cli-overview/xygeni-cli-installation. This bypasses the GitHub Action entirely and is not affected by this incident.
References
- GitHub issue: https://github.com/xygeni/xygeni-action/issues/54
- Xygeni incident blog post: (URL to be added upon publication)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦GitHub Actions | xygeni/xygeni-action | ≥ 5&&< 6.4.0 | 6.4.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for xygeni/xygeni-action, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update xygeni/xygeni-action to 6.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-31976 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-31976 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-31976. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-31976 in your dependencies?
O3 Security finds CVE-2026-31976 across GitHub Actions dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.