---
title: "CVE-2026-31976: xygeni-action v5 tag poisoned with C2 backdoor"
url: https://erroneo.us/security/cve/CVE-2026-31976/
description: "CVE-2026-31976 (xygeni/xygeni-action (GitHub Actions)): xygeni-action is the GitHub Action for Xygeni Scanner. On March 3, 2026, an attacker with access to…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-03-11
date_modified: 2026-03-12
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-31976"
kev: false
cvss: 9.3
epss: 0.0086
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.9% , percentile 58: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 58% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes xygeni/xygeni-action (GitHub Actions) >= 5, < 6.4.0, fixed in 6.4.0 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- GitHub Actions `xygeni/xygeni-action` >= 5, < 6.4.0 → fixed: 6.4.0

## Affected products (CVE record)

- xygeni xygeni-action: >= March 3, 2026, <= March 10, 2026

## Severity

- GitHub_M CVSS 4.0: 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`
- GitHub CVSS 4.0: 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`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.86% probability of exploitation activity in the next 30 days; percentile 58.

## Sources

- [GitHub Advisory GHSA-f8q5-h5qh-33mh](https://github.com/advisories/GHSA-f8q5-h5qh-33mh)
- [CVE.org record CVE-2026-31976](https://www.cve.org/CVERecord?id=CVE-2026-31976)
- [NVD entry CVE-2026-31976](https://nvd.nist.gov/vuln/detail/CVE-2026-31976)
- [github.com](https://github.com/xygeni/xygeni-action/security/advisories/GHSA-f8q5-h5qh-33mh)
- [github.com](https://github.com/xygeni/xygeni-action/issues/54)

---
Source page: https://erroneo.us/security/cve/CVE-2026-31976/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt