java-native-access/jna · error · IllegalArgumentException

Missing variable value separator in

Error message

Missing variable value separator in 

What it means

Kernel32Util.getEnvironmentVariables throws this IllegalArgumentException when an entry of the remote/process environment block has no '=' separator between the variable name and value. Well-formed environment entries always contain '=', so a missing separator means a malformed environment block was read.

Source

Thrown at contrib/platform/src/com/sun/jna/platform/win32/Kernel32Util.java:486

     */
    public static Map<String,String> getEnvironmentVariables(Pointer lpszEnvironmentBlock, long offset) {
        if (lpszEnvironmentBlock == null) {
            return null;
        }

        Map<String,String>  vars=new TreeMap<>();
        boolean             asWideChars=isWideCharEnvironmentStringBlock(lpszEnvironmentBlock, offset);
        long                stepFactor=asWideChars ? 2L : 1L;
        for (long    curOffset=offset; ; ) {
            String  nvp=readEnvironmentStringBlockEntry(lpszEnvironmentBlock, curOffset, asWideChars);
            int     len=nvp.length();
            if (len == 0) { // found the ending '\0'
                break;
            }

            int pos=nvp.indexOf('=');
            if (pos < 0) {
                throw new IllegalArgumentException("Missing variable value separator in " + nvp);
            }

            String  name=nvp.substring(0, pos), value=nvp.substring(pos + 1);
            vars.put(name, value);

            curOffset += (len + 1 /* skip the ending '\0' */) * stepFactor;
        }

        return vars;
    }

    /**
     * @param lpszEnvironmentBlock The environment block as received from the
     * <A HREF="https://msdn.microsoft.com/en-us/library/windows/desktop/ms683187(v=vs.85).aspx">GetEnvironmentStrings</A>
     * function
     * @param offset Offset within the block to look for the entry
     * @param asWideChars If {@code true} then the block contains {@code wchar_t}
     * instead of &quot;plain old&quot; {@code char}s

View on GitHub (pinned to d036ad9781)

Solutions

1. Ensure the correct string width (stepFactor) is used for the target process (Unicode vs ANSI, 32 vs 64-bit)
2. Re-read the environment block atomically; the target may have mutated it during the scan (retry, possibly with the process suspended)
3. Validate the base address of the environment block (ProcessParameters.Environment) before iterating; a wrong base yields garbage entries
4. If an entry is genuinely malformed, wrap the call in try-catch for IllegalArgumentException and skip/log the offending environment

Example fix

// before
Map<String,String> env = Kernel32Util.getEnvironmentVariables(hProcess, envAddress);
// after
try {
    Map<String,String> env = Kernel32Util.getEnvironmentVariables(hProcess, envAddress);
} catch (IllegalArgumentException e) {
    // malformed environment block (mutated or wrong string width)
    log.warn("Failed to read environment block: " + e.getMessage());
}

try {
    Map<String,String> env = Kernel32Util.getEnvironmentVariables(hProcess, address);
} catch (IllegalArgumentException e) {
    if (e.getMessage().startsWith("Missing variable value separator")) {
        // environment block mutated or wrong string width: suspend target and retry
        Map<String,String> env = Kernel32Util.getEnvironmentVariables(hProcess, address);
    } else {
        throw e;
    }
}

When it happens

Trigger: Reading another process's environment block (via getEnvironmentVariables on a Process handle) where the memory layout was parsed incorrectly — commonly a Unicode/ANSI (stepFactor) mismatch or corrupted entry boundaries; entries like empty or malformed strings returned by the target process.

Common situations: Cross-architecture (32/64-bit) reading of PEB environment; reading a process whose environment was modified while being scanned; passing a step size that misaligns string boundaries.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Window width and/or height were 0 even though GetWindowRect
• Device context did not release properly.
• Invalid data length:
• Invalid guid length:
• FileMonitor not implemented for " + os

AI-assisted analysis of java-native-access/jna@d036ad9781 (2026-09-12). Data as JSON: /api/errors/0c46e3a95d9fe975. Report an issue: GitHub.