# CVE-2026-31976: xygeni-action v5 tag poisoned with C2 backdoor

> Attackers poisoned a GitHub Action tag to inject a backdoor, allowing arbitrary command execution on CI runners for workflows using the compromised version.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Mar 2026
- **Updated:** 12 Mar 2026
- **Also known as:** GHSA-f8q5-h5qh-33mh

## What is CVE-2026-31976?

CVE-2026-31976 is a critical vulnerability in xygeni-action, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

xygeni-action is the GitHub Action for Xygeni Scanner. 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. 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.

Weakness: CWE-506 (Embedded Malicious Code)

## Which versions are affected by CVE-2026-31976?

1 open source package ship an affected version, including xygeni/xygeni-action. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `xygeni/xygeni-action` | GitHub Actions | From 5 | 6.4.0 |

Products: Xygeni Xygeni-Action.

## How do I fix CVE-2026-31976?

Upgrade xygeni/xygeni-action to 6.4.0 or later.

## Is CVE-2026-31976 being exploited?

There is no known exploitation of CVE-2026-31976 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31976 and fix it if it is affected.

What it is: CVE-2026-31976 is a critical vulnerability in xygeni-action, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-31976 in the wild and no public exploit code.

Affected packages and fixed versions:
- xygeni/xygeni-action (GitHub Actions): affected from 5; fixed in 6.4.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-31976/ (Markdown: https://insights.sbomify.com/CVE-2026-31976/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31976
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31976
- OSV: https://osv.dev/vulnerability/CVE-2026-31976

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31976/
Summaries are generated and may contain mistakes; the official description above is the record.