fix: tighten shell wrapper detection

Use exact matches for known shell wrappers so command display and approval keys do not treat arbitrary shell-like paths as trusted wrappers.

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/command_canonicalization_tests.rs

@@ -86,3 +86,14 @@ fn preserves_non_shell_commands() {
     let command = vec!["cargo".to_string(), "fmt".to_string()];
     assert_eq!(canonicalize_command_for_approval(&command), command);
 }
+
+#[test]
+fn preserves_shell_like_paths_in_approval_keys() {
+    let command = vec![
+        ".poc/bash".to_string(),
+        "-lc".to_string(),
+        "cargo test -p codex-core".to_string(),
+    ];
+
+    assert_eq!(canonicalize_command_for_approval(&command), command);
+}

codex-rs/core/src/shell.rs

@@ -367,6 +367,9 @@ mod detect_shell_type_tests {
             detect_shell_type(&PathBuf::from("/bin/bash")),
             Some(ShellType::Bash)
         );
+        assert_eq!(detect_shell_type(&PathBuf::from(".poc/bash")), None);
+        assert_eq!(detect_shell_type(&PathBuf::from("/tmp/bash")), None);
+        assert_eq!(detect_shell_type(&PathBuf::from("/tmp/bash.evil")), None);
         assert_eq!(
             detect_shell_type(&PathBuf::from("powershell.exe")),
             Some(ShellType::PowerShell)
@@ -401,6 +404,12 @@ mod detect_shell_type_tests {
             Some(ShellType::Cmd)
         );
     }
+
+    #[test]
+    fn model_provided_shell_does_not_accept_repo_local_shell_names() {
+        let shell = get_shell_by_model_provided_path(&PathBuf::from(".poc/bash"));
+        assert_ne!(shell.shell_path, PathBuf::from(".poc/bash"));
+    }
 }
 
 #[cfg(test)]

codex-rs/core/src/shell_detect.rs

@@ -1,24 +1,34 @@
 use crate::shell::ShellType;
-use std::path::Path;
 use std::path::PathBuf;
 
 pub(crate) fn detect_shell_type(shell_path: &PathBuf) -> Option<ShellType> {
-    match shell_path.as_os_str().to_str() {
-        Some("zsh") => Some(ShellType::Zsh),
-        Some("sh") => Some(ShellType::Sh),
-        Some("cmd") => Some(ShellType::Cmd),
-        Some("bash") => Some(ShellType::Bash),
-        Some("pwsh") => Some(ShellType::PowerShell),
-        Some("powershell") => Some(ShellType::PowerShell),
-        _ => {
-            let shell_name = shell_path.file_stem();
-            if let Some(shell_name) = shell_name {
-                let shell_name_path = Path::new(shell_name);
-                if shell_name_path != Path::new(shell_path) {
-                    return detect_shell_type(&shell_name_path.to_path_buf());
-                }
-            }
-            None
+    let shell_text = shell_path.as_os_str().to_str()?;
+    // Keep this exact: repo-local files named like shells must not inherit
+    // shell-wrapper trust in approval or display decisions.
+    match shell_text {
+        "zsh" | "/bin/zsh" | "/usr/bin/zsh" | "/usr/local/bin/zsh" | "/opt/homebrew/bin/zsh" => {
+            Some(ShellType::Zsh)
         }
+        "sh" | "/bin/sh" | "/usr/bin/sh" => Some(ShellType::Sh),
+        "bash"
+        | "/bin/bash"
+        | "/usr/bin/bash"
+        | "/usr/local/bin/bash"
+        | "/opt/homebrew/bin/bash" => Some(ShellType::Bash),
+        "pwsh"
+        | "powershell"
+        | "pwsh.exe"
+        | "powershell.exe"
+        | "/usr/local/bin/pwsh"
+        | "/usr/bin/pwsh"
+        | "/bin/pwsh"
+        | "/opt/homebrew/bin/pwsh" => Some(ShellType::PowerShell),
+        "cmd" | "cmd.exe" => Some(ShellType::Cmd),
+        _ => match shell_text.replace('\\', "/").to_ascii_lowercase().as_str() {
+            "c:/windows/system32/cmd.exe" => Some(ShellType::Cmd),
+            "c:/windows/system32/windowspowershell/v1.0/powershell.exe"
+            | "c:/program files/powershell/7/pwsh.exe" => Some(ShellType::PowerShell),
+            _ => None,
+        },
     }
 }

codex-rs/core/src/tools/handlers/unified_exec_tests.rs

@@ -68,6 +68,27 @@ fn test_get_command_respects_explicit_bash_shell() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_get_command_does_not_execute_shell_like_repo_path() -> anyhow::Result<()> {
+    let json = r#"{"cmd": "echo hello", "shell": ".poc/bash"}"#;
+
+    let args: ExecCommandArgs = parse_arguments(json)?;
+
+    assert_eq!(args.shell.as_deref(), Some(".poc/bash"));
+
+    let command = get_command(
+        &args,
+        Arc::new(default_user_shell()),
+        &UnifiedExecShellMode::Direct,
+        /*allow_login_shell*/ true,
+    )
+    .map_err(anyhow::Error::msg)?;
+
+    assert_ne!(command.first(), Some(&".poc/bash".to_string()));
+    assert_eq!(command.last(), Some(&"echo hello".to_string()));
+    Ok(())
+}
+
 #[test]
 fn test_get_command_respects_explicit_powershell_shell() -> anyhow::Result<()> {
     let json = r#"{"cmd": "echo hello", "shell": "powershell"}"#;

codex-rs/shell-command/src/bash.rs

@@ -453,6 +453,18 @@ mod tests {
         assert_eq!(parsed, vec![vec!["ls".to_string()]]);
     }
 
+    #[test]
+    fn extract_bash_command_rejects_shell_like_attacker_paths() {
+        for shell in [".poc/bash", "/tmp/bash", "/tmp/bash.evil"] {
+            let command = vec![
+                shell.to_string(),
+                "-lc".to_string(),
+                "echo INNOCENT_COMMAND".to_string(),
+            ];
+            assert_eq!(extract_bash_command(&command), None);
+        }
+    }
+
     #[test]
     fn accepts_concatenated_flag_and_value() {
         // Test case: -g"*.py" (flag directly concatenated with quoted value)

codex-rs/shell-command/src/parse_command.rs

@@ -1260,7 +1260,7 @@ mod tests {
         let command = if cfg!(windows) {
             "C:\\windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe"
         } else {
-            "/usr/local/bin/powershell.exe"
+            "/usr/local/bin/pwsh"
         };
 
         assert_parsed(

codex-rs/shell-command/src/powershell.rs

@@ -168,13 +168,23 @@ mod tests {
         let command = if cfg!(windows) {
             "C:\\windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe".to_string()
         } else {
-            "/usr/local/bin/powershell.exe".to_string()
+            "/usr/local/bin/pwsh".to_string()
         };
         let cmd = vec![command, "-Command".to_string(), "Write-Host hi".to_string()];
         let (_shell, script) = extract_powershell_command(&cmd).expect("extract");
         assert_eq!(script, "Write-Host hi");
     }
 
+    #[test]
+    fn rejects_shell_like_attacker_paths() {
+        let cmd = vec![
+            r"C:\tmp\powershell.exe".to_string(),
+            "-Command".to_string(),
+            "Write-Host hi".to_string(),
+        ];
+        assert_eq!(extract_powershell_command(&cmd), None);
+    }
+
     #[test]
     fn extracts_with_noprofile_and_alias() {
         let cmd = vec![

codex-rs/shell-command/src/shell_detect.rs

@@ -1,4 +1,3 @@
-use std::path::Path;
 use std::path::PathBuf;
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
@@ -11,22 +10,71 @@ pub(crate) enum ShellType {
 }
 
 pub(crate) fn detect_shell_type(shell_path: &PathBuf) -> Option<ShellType> {
-    match shell_path.as_os_str().to_str() {
-        Some("zsh") => Some(ShellType::Zsh),
-        Some("sh") => Some(ShellType::Sh),
-        Some("cmd") => Some(ShellType::Cmd),
-        Some("bash") => Some(ShellType::Bash),
-        Some("pwsh") => Some(ShellType::PowerShell),
-        Some("powershell") => Some(ShellType::PowerShell),
-        _ => {
-            let shell_name = shell_path.file_stem();
-            if let Some(shell_name) = shell_name {
-                let shell_name_path = Path::new(shell_name);
-                if shell_name_path != Path::new(shell_path) {
-                    return detect_shell_type(&shell_name_path.to_path_buf());
-                }
-            }
-            None
+    let shell_text = shell_path.as_os_str().to_str()?;
+    // Keep this exact: repo-local files named like shells must not inherit
+    // shell-wrapper trust in approval or display decisions.
+    match shell_text {
+        "zsh" | "/bin/zsh" | "/usr/bin/zsh" | "/usr/local/bin/zsh" | "/opt/homebrew/bin/zsh" => {
+            Some(ShellType::Zsh)
         }
+        "sh" | "/bin/sh" | "/usr/bin/sh" => Some(ShellType::Sh),
+        "bash"
+        | "/bin/bash"
+        | "/usr/bin/bash"
+        | "/usr/local/bin/bash"
+        | "/opt/homebrew/bin/bash" => Some(ShellType::Bash),
+        "pwsh"
+        | "powershell"
+        | "pwsh.exe"
+        | "powershell.exe"
+        | "/usr/local/bin/pwsh"
+        | "/usr/bin/pwsh"
+        | "/bin/pwsh"
+        | "/opt/homebrew/bin/pwsh" => Some(ShellType::PowerShell),
+        "cmd" | "cmd.exe" => Some(ShellType::Cmd),
+        _ => match shell_text.replace('\\', "/").to_ascii_lowercase().as_str() {
+            "c:/windows/system32/cmd.exe" => Some(ShellType::Cmd),
+            "c:/windows/system32/windowspowershell/v1.0/powershell.exe"
+            | "c:/program files/powershell/7/pwsh.exe" => Some(ShellType::PowerShell),
+            _ => None,
+        },
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn detects_exact_shell_names_and_system_paths() {
+        assert_eq!(
+            detect_shell_type(&PathBuf::from("bash")),
+            Some(ShellType::Bash)
+        );
+        assert_eq!(
+            detect_shell_type(&PathBuf::from("/bin/bash")),
+            Some(ShellType::Bash)
+        );
+        assert_eq!(
+            detect_shell_type(&PathBuf::from("powershell.exe")),
+            Some(ShellType::PowerShell)
+        );
+        assert_eq!(
+            detect_shell_type(&PathBuf::from(
+                r"C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe"
+            )),
+            Some(ShellType::PowerShell)
+        );
+    }
+
+    #[test]
+    fn rejects_shell_like_attacker_controlled_paths() {
+        assert_eq!(detect_shell_type(&PathBuf::from(".poc/bash")), None);
+        assert_eq!(detect_shell_type(&PathBuf::from("/tmp/bash")), None);
+        assert_eq!(detect_shell_type(&PathBuf::from("/tmp/bash.evil")), None);
+        assert_eq!(
+            detect_shell_type(&PathBuf::from(r"C:\tmp\powershell.exe")),
+            None
+        );
     }
 }

codex-rs/tui/src/exec_command.rs

@@ -82,6 +82,10 @@ mod tests {
         let args = vec!["/bin/bash".into(), "-lc".into(), "echo hello".into()];
         let cmdline = strip_bash_lc_and_escape(&args);
         assert_eq!(cmdline, "echo hello");
+
+        let args = vec![".poc/bash".into(), "-lc".into(), "echo hello".into()];
+        let cmdline = strip_bash_lc_and_escape(&args);
+        assert_eq!(cmdline, ".poc/bash -lc 'echo hello'");
     }
 
     #[test]