Executive brief
githubtoplanguages is a GitHub tool that generates SVG visualizations of a user's top programming languages. A flaw in its Discord notification workflow allows attackers to execute arbitrary shell commands on the GitHub Actions runner by crafting a malicious issue title. This can expose workflow secrets (like Discord webhooks) or be used to send fraudulent notifications.
Technical details
The vulnerability is an OS command injection (CWE-78) in the .github/workflows/discord-issue.yml workflow. The workflow directly interpolates the GitHub event issue title (github.event.issue.title) into a Bash variable assignment without proper quoting: ISSUE_TITLE="${{ github.event.issue.title }}". Since GitHub Actions expressions are expanded before Bash execution, an attacker can inject command substitution syntax (e.g., $(whoami)) in the issue title to execute arbitrary commands on the runner. No authentication is required beyond the ability to open an issue in the repository. Successful exploitation allows command execution in the workflow environment, potentially exposing the Discord webhook secret and other sensitive environment variables. The fix (commit 6bf9c3a) properly escapes the variable assignment using environment variable passing instead of direct interpolation.
Affected products
- gouef githubtoplanguages
Timeline
- 2026-09-15: disclosed
- 2026-09-15: patched: Fixed in commit 6bf9c3a9cb66c937b9047ca266b3d02f2bb11027