What causes "str" in peass-ng/PEASS-ng?

Ensure the string is non-null before calling the decode API (coalesce to empty string or reject).

peass-ng/PEASS-ng · error · ArgumentNullException

str

Error message

str

What it means

HexEncoder.DecodeStrict is the internal strict hex decoder. It validates arguments before decoding: a null string throws ArgumentNullException with param name 'str'. The library throws this to fail fast on a null input instead of throwing NullReferenceException deep inside the decode loop.

Source

Thrown at winPEAS/winPEASexe/winPEAS/3rdParty/BouncyCastle/util/encoders/HexEncoder.cs:219

                    outStream.Write(buf, 0, bufOff);
                    bufOff = 0;
                }

                length++;
            }

            if (bufOff > 0)
            {
                outStream.Write(buf, 0, bufOff);
            }

            return length;
        }

        internal byte[] DecodeStrict(string str, int off, int len)
        {
            if (null == str)
                throw new ArgumentNullException("str");
            if (off < 0 || len < 0 || off > (str.Length - len))
                throw new IndexOutOfRangeException("invalid offset and/or length specified");
            if (0 != (len & 1))
                throw new ArgumentException("a hexadecimal encoding must have an even number of characters", "len");

            int resultLen = len >> 1;
            byte[] result = new byte[resultLen];

            int strPos = off;
            for (int i = 0; i < resultLen; ++i)
            {
                byte b1 = decodingTable[str[strPos++]];
                byte b2 = decodingTable[str[strPos++]];

                if ((b1 | b2) >= 0x80)
                    throw new IOException("invalid characters encountered in Hex data");

                result[i] = (byte)((b1 << 4) | b2);

View on GitHub (pinned to 53fb989abc)

Solutions

Ensure the string is non-null before calling the decode API (coalesce to empty string or reject).
Add an explicit null check with a meaningful error at your boundary.
Catch ArgumentNullException and report which input was missing.

Example fix

// before
var bytes = Hex.Decode(str); // str is null
// after
if (str == null) throw new InvalidOperationException("hex input was not provided");
var bytes = Hex.Decode(str);

Defensive patterns

Strategy: type-guard

Validate before calling

if (string.IsNullOrEmpty(str)) throw new ArgumentException("hex input required", nameof(str));

Type guard

static bool IsDecodableHex(string s) => !string.IsNullOrEmpty(s) && s.Length % 2 == 0 && s.All(Uri.IsHexDigit);

Try / catch

try { decodeStrict(str, 0, str.Length); } catch (ArgumentNullException) { return Array.Empty<byte>(); }

Prevention

Initialize hex string variables at declaration
Fail early at input boundaries with explicit null checks
Use non-null assertions/nullable annotations to catch nulls at compile time

When it happens

Trigger: Calling an internal/reflective path that passes a null string to DecodeStrict(string str, int off, int len) — e.g. Hex.Decode with a null argument on strict-mode overloads.

Common situations: Variables that were never assigned from parsed input; deserialization producing null strings; API callers not honoring the non-null contract.

Related errors

AI-assisted analysis of peass-ng/PEASS-ng@53fb989abc (2026-09-02). Data as JSON: /api/errors/1a8c605b9545aa01. Report an issue: GitHub.