GitHub Copilot CLI Dangerous Shell Expansion Patterns Enable Arbitrary Code Execution

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.5 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-29783: 0.47% estimated exploitation activity in the next 30 days; percentile 40.58 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A security vulnerability has been identified in GitHub Copilot CLI's shell tool that could allow arbitrary code execution through crafted bash parameter expansion patterns. An attacker who can influence the commands executed by the agent (e.g., via prompt injection through repository files, MCP server responses, or user instructions) can exploit bash parameter transformation operators to execute hidden commands, bypassing the safety assessment that classifies commands as "read-only." Details The vulnerability stems from how the CLI's shell safety assessment evaluates commands before execution. The safety layer parses and classifies shell commands as either read-only (safe) or write-capable (requires user approval). However, several bash parameter expansion features can embed executable code within arguments to otherwise read-only commands, causing them to appear safe while actually performing arbitrary operations. The specific dangerous patterns are: 1. ${var@P} — Prompt…

Published by the source

6 Mar 2026, 16:43 UTC

Last modified by the source

13 Mar 2026, 16:36 UTC

Source last checked

26 Oct 2026, 12:46 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-g8r9-g2v8-jv6f

2. Revision 2 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-g8r9-g2v8-jv6f

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# Patch Next advisory brief: CVE-2026-29783

Advisory: GitHub Copilot CLI Dangerous Shell Expansion Patterns Enable Arbitrary Code Execution
IDs: CVE-2026-29783, GHSA-g8r9-g2v8-jv6f
Record: https://patchnext.com/advisories/cve-2026-29783 (revision 3, source checked 26 Oct 2026, 12:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @github/copilot 0.0.423. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @github/copilot: affected <= 0.0.422; fixed in 0.0.423

## Suggested inspection (read-only)
- `npm ls @github/copilot --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @github/copilot.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-g8r9-g2v8-jv6f (OSV record GHSA-g8r9-g2v8-jv6f lists affected ranges: npm @github/copilot >=0 <0.0.423 (fixed))
- Verified: https://github.com/advisories/GHSA-g8r9-g2v8-jv6f (GitHub-reviewed advisory GHSA-g8r9-g2v8-jv6f lists affected ranges: npm @github/copilot >=0 <=0.0.422)

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