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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: herdr maintainers <maintainers@herdr.dev>
Date: Tue, 1 Sep 2026 00:00:00 +0000
Subject: [PATCH] reject malformed Windows process environments
Windows registry environment keys can contain empty names, non-string types,
or malformed UTF-16. Decode string values into aligned storage, check Win32
expansion failures, preserve valid drive variables, and omit entries that
cannot form a valid environment record before calling CreateProcessW.
Herdr issue: https://github.com/herdrdev/herdr/issues/3430
Vendored base: portable-pty 0.9.0
---
diff --git a/vendor/portable-pty/src/cmdbuilder.rs b/vendor/portable-pty/src/cmdbuilder.rs
index 385fe81c..b214bb6d 100644
--- a/vendor/portable-pty/src/cmdbuilder.rs
+++ b/vendor/portable-pty/src/cmdbuilder.rs
@@ -71,6 +71,70 @@ fn get_shell() -> String {
"/bin/sh".into()
}
+#[cfg(windows)]
+fn reg_value_to_string(value: &winreg::RegValue) -> anyhow::Result<OsString> {
+ use std::os::windows::ffi::OsStringExt;
+ use winapi::um::processenv::ExpandEnvironmentStringsW;
+ use winreg::enums::RegType;
+
+ if !matches!(value.vtype, RegType::REG_SZ | RegType::REG_EXPAND_SZ) {
+ anyhow::bail!(
+ "unsupported registry type {:?} for environment variable",
+ value.vtype
+ );
+ }
+
+ let mut bytes = value.bytes.chunks_exact(2);
+ let mut units: Vec<u16> = bytes
+ .by_ref()
+ .map(|pair| u16::from_le_bytes([pair[0], pair[1]]))
+ .collect();
+ anyhow::ensure!(
+ bytes.remainder().is_empty(),
+ "invalid UTF-16 byte length for environment variable"
+ );
+ while let Some(0) = units.last() {
+ units.pop();
+ }
+ anyhow::ensure!(
+ !units.contains(&0),
+ "embedded null in registry environment variable"
+ );
+
+ if value.vtype == RegType::REG_SZ {
+ return Ok(OsString::from_wide(&units));
+ }
+
+ units.push(0);
+ let size = unsafe { ExpandEnvironmentStringsW(units.as_ptr(), std::ptr::null_mut(), 0) };
+ if size == 0 {
+ anyhow::bail!(
+ "ExpandEnvironmentStringsW failed: {}",
+ std::io::Error::last_os_error()
+ );
+ }
+ let mut buf = vec![0u16; size as usize];
+ let written = unsafe {
+ ExpandEnvironmentStringsW(units.as_ptr(), buf.as_mut_ptr(), buf.len() as u32)
+ };
+ if written == 0 {
+ anyhow::bail!(
+ "ExpandEnvironmentStringsW failed: {}",
+ std::io::Error::last_os_error()
+ );
+ }
+ anyhow::ensure!(
+ written as usize <= buf.len(),
+ "environment changed while expanding registry value"
+ );
+
+ buf.truncate(written as usize);
+ while let Some(0) = buf.last() {
+ buf.pop();
+ }
+ Ok(OsString::from_wide(&buf))
+}
+
fn get_base_env() -> BTreeMap<OsString, EnvEntry> {
let mut env: BTreeMap<OsString, EnvEntry> = std::env::vars_os()
.map(|(key, value)| {
@@ -103,37 +167,8 @@ fn get_base_env() -> BTreeMap<OsString, EnvEntry> {
#[cfg(windows)]
{
- use std::os::windows::ffi::OsStringExt;
- use winapi::um::processenv::ExpandEnvironmentStringsW;
- use winreg::enums::{RegType, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE};
- use winreg::types::FromRegValue;
- use winreg::{RegKey, RegValue};
-
- fn reg_value_to_string(value: &RegValue) -> anyhow::Result<OsString> {
- match value.vtype {
- RegType::REG_EXPAND_SZ => {
- let src = unsafe {
- std::slice::from_raw_parts(
- value.bytes.as_ptr() as *const u16,
- value.bytes.len() / 2,
- )
- };
- let size =
- unsafe { ExpandEnvironmentStringsW(src.as_ptr(), std::ptr::null_mut(), 0) };
- let mut buf = vec![0u16; size as usize + 1];
- unsafe {
- ExpandEnvironmentStringsW(src.as_ptr(), buf.as_mut_ptr(), buf.len() as u32)
- };
-
- let mut buf = buf.as_slice();
- while let Some(0) = buf.last() {
- buf = &buf[0..buf.len() - 1];
- }
- Ok(OsString::from_wide(buf))
- }
- _ => Ok(OsString::from_reg_value(value)?),
- }
- }
+ use winreg::enums::{HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE};
+ use winreg::RegKey;
if let Ok(sys_env) = RegKey::predef(HKEY_LOCAL_MACHINE)
.open_subkey("System\\CurrentControlSet\\Control\\Session Manager\\Environment")
@@ -662,12 +697,24 @@ impl CommandBuilder {
value,
} in self.envs.values()
{
- block.extend(preferred_key.encode_wide());
+ let key: Vec<u16> = preferred_key.encode_wide().collect();
+ if key.is_empty()
+ || key.contains(&0)
+ || key[1..].contains(&(b'=' as u16))
+ || value.encode_wide().any(|unit| unit == 0)
+ {
+ continue;
+ }
+
+ block.extend(key);
block.push(b'=' as u16);
block.extend(value.encode_wide());
block.push(0);
}
// and a final terminator for CreateProcessW
+ if block.is_empty() {
+ block.push(0);
+ }
block.push(0);
block
@@ -869,4 +916,65 @@ mod tests {
cmd.env_remove("cARGO_pKG_aUTHORS");
assert!(cmd.get_env("CARGO_PKG_AUTHORS").is_none());
}
+
+ #[cfg(windows)]
+ #[test]
+ fn windows_environment_rejects_malformed_entries() {
+ use std::os::windows::ffi::{OsStrExt, OsStringExt};
+ use winreg::enums::RegType;
+ use winreg::RegValue;
+
+ let multi_string = RegValue {
+ bytes: vec![b'a', 0, 0, 0],
+ vtype: RegType::REG_MULTI_SZ,
+ };
+ assert!(reg_value_to_string(&multi_string).is_err());
+ let malformed_expand_string = RegValue {
+ bytes: vec![b'%', 0, b'P'],
+ vtype: RegType::REG_EXPAND_SZ,
+ };
+ assert!(reg_value_to_string(&malformed_expand_string).is_err());
+ let expandable_string = RegValue {
+ bytes: "literal\0"
+ .encode_utf16()
+ .flat_map(u16::to_le_bytes)
+ .collect(),
+ vtype: RegType::REG_EXPAND_SZ,
+ };
+ assert_eq!(
+ reg_value_to_string(&expandable_string).unwrap(),
+ OsString::from("literal")
+ );
+
+ let mut cmd = CommandBuilder::new("dummy");
+ cmd.env_clear();
+ cmd.env("", "ignored");
+ cmd.env(
+ OsString::from_wide(&[b'B' as u16, 0, b'A' as u16, b'D' as u16]),
+ "ignored",
+ );
+ cmd.env(
+ "MULTI",
+ OsString::from_wide(&[b'a' as u16, 0, b'b' as u16]),
+ );
+ cmd.env("BAD=KEY", "ignored");
+ cmd.env("=::", "colon");
+ cmd.env("=C:", r"C:\valid");
+ cmd.env("=ExitCode", "hidden");
+ cmd.env("EMPTY", "");
+ cmd.env("VALID", "ok");
+
+ let expected: Vec<u16> =
+ OsStr::new("=::=colon\0=C:=C:\\valid\0=ExitCode=hidden\0EMPTY=\0VALID=ok\0\0")
+ .encode_wide()
+ .collect();
+ assert_eq!(cmd.environment_block(), expected);
+
+ cmd.env_remove("=::");
+ cmd.env_remove("=C:");
+ cmd.env_remove("=ExitCode");
+ cmd.env_remove("EMPTY");
+ cmd.env_remove("VALID");
+ assert_eq!(cmd.environment_block(), vec![0, 0]);
+ }
}
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