---
title: "CVE-2026-55158: conflibot vulnerable to command injection via crafted pull request branch names under pull_request_target"
url: https://erroneo.us/security/cve/CVE-2026-55158/
description: "CVE-2026-55158 (wktk/conflibot (GitHub Actions)): Conflibot warns in advance when merging a pull request will cause conflicts in other open pull requests.…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-09-15
date_modified: 2026-09-17
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-55158"
kev: false
cvss: 9.1
epss: 0.00804
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-55158: conflibot vulnerable to command injection via crafted pull request branch names under pull_request_target

**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 0.8% , percentile 56: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 56% 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 wktk/conflibot (GitHub Actions) < 1.2.1, fixed in 1.2.1 . Check your lockfile, including transitive dependencies.

## What it is

Conflibot warns in advance when merging a pull request will cause conflicts in other open pull requests. Prior to 1.2.1, src/index.ts builds git checkout, git merge, and git format-patch commands by interpolating the attacker-controlled pull request head.ref value into strings passed to exec. In the documented pullrequesttarget configuration, an attacker can open a pull request, including from a fork, whose branch name contains shell metacharacters, and the workflow automatically interprets those characters as commands without maintainer interaction. The commands execute on a runner with base-repository secrets and a write-scoped GITHUBTOKEN, allowing arbitrary command execution, secret or token exfiltration, unauthorized pushes, and other token abuse. The fixed implementations in src/index.ts and src/conflibot.ts use execFile or spawn argument arrays, and the v2 line also uses numeric pull-request refs rather than branch names. This issue is fixed in versions 1.2.1 and 2.0.0.

## Affected packages

- GitHub Actions `wktk/conflibot` < 1.2.1 → fixed: 1.2.1

## Affected products (CVE record)

- wktk conflibot: < 1.2.1

## Severity

- GitHub_M CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`
- GitHub CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A: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): 0.80% probability of exploitation activity in the next 30 days; percentile 56.

## Sources

- [GitHub Advisory GHSA-2qvg-qr73-mqxp](https://github.com/advisories/GHSA-2qvg-qr73-mqxp)
- [CVE.org record CVE-2026-55158](https://www.cve.org/CVERecord?id=CVE-2026-55158)
- [NVD entry CVE-2026-55158](https://nvd.nist.gov/vuln/detail/CVE-2026-55158)
- [github.com](https://github.com/wktk/conflibot/security/advisories/GHSA-2qvg-qr73-mqxp)
- [github.com](https://github.com/wktk/conflibot/pull/329)
- [github.com](https://github.com/wktk/conflibot/commit/0107ac6a4575ea200d0b92287ea58f975be9505d)
- [github.com](https://github.com/wktk/conflibot/commit/59e255c49c920fd6b67471ab9ef3bf194439a3f2)
- [github.com](https://github.com/wktk/conflibot/releases/tag/v1.2.1)
- [github.com](https://github.com/wktk/conflibot/releases/tag/v2.0.0)
- [github.com](https://github.com/wktk/conflibot/commit/0107ac6)
- [github.com](https://github.com/wktk/conflibot/commit/59e255c)

---
Source page: https://erroneo.us/security/cve/CVE-2026-55158/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt