# CVE-2026-55158

## Summary

- **CVE ID:** CVE-2026-55158
- **Severity:** CRITICAL
- **CVSS Score:** 9.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N)
- **CWE:** CWE-78
- **Published:** Sep 15, 2026
- **Last Modified:** Sep 17, 2026

## Description

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 pull_request_target 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 GITHUB_TOKEN, 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 Products

- wktk — conflibot (< 1.2.1)

## References

- [CNA](https://github.com/wktk/conflibot/pull/329)
- [CNA](https://github.com/wktk/conflibot/security/advisories/GHSA-2qvg-qr73-mqxp)
- [CNA](https://github.com/wktk/conflibot/commit/0107ac6a4575ea200d0b92287ea58f975be9505d)
- [CNA](https://github.com/wktk/conflibot/commit/59e255c49c920fd6b67471ab9ef3bf194439a3f2)
- [CNA](https://github.com/wktk/conflibot/releases/tag/v1.2.1)
- [CNA](https://github.com/wktk/conflibot/releases/tag/v2.0.0)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.45%
- **EPSS Percentile:** 37.8

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._