The shell tool within GitHub Copilot CLI versions prior to and including 0.0.422 can 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." This has been patched in version 0.0.423. 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 ${var@P}, ${var=value} / ${var:=value}, ${!var}, and nested $(cmd) or <(cmd) inside ${...} expansions. An attacker who can influence command text sent to the shell tool - for example, through prompt injection via malicious repository content (README files, code comments, issue bodies), compromised or malicious MCP server responses, or crafted user instructions containing obfuscated commands - could achieve arbitrary code execution on the user's workstation. This is possible even in permission modes that require user approval for write operations, since the commands can appear to use only read-only utilities to ultimately trigger write operations. Successful exploitation could lead to data exfiltration, file modification, or further system compromise.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - The shell tool within GitHub Copilot CLI versions prior to and including 0.0.422 can 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." This has been patched in version 0.0.423.
    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 ${var@P}, ${var=value} / ${var:=value}, ${!var},
    and nested $(cmd) or <(cmd) inside ${...} expansions. An attacker who can influence command text sent to
    the shell tool - for example, through prompt injection via malicious repository content (README files,
    code comments, issue bodies), compromised or malicious MCP server responses, or crafted user instructions
    containing obfuscated commands - could achieve arbitrary code execution on the user's workstation. This is
    possible even in permission modes that require user approval for write operations, since the commands can
    appear to use only read-only utilities to ultimately trigger write operations. Successful exploitation
    could lead to data exfiltration, file modification, or further system compromise. (CVE-2026-29783)

ID	Name	Product	Family	Severity
438448	SCA: security update for @github/copilot (GHSA-g8r9-g2v8-jv6f)	Tenable Cloud Security	SCA Checks	high
438448	SCA: security update for @github/copilot (GHSA-g8r9-g2v8-jv6f)	Tenable Self-Hosted Container Security	SCA Checks	high

Detections

Analytics

CVE-2026-29783

high

Tenable Plugins

high

high