jstedfast/MailKit · error · ArgumentOutOfRangeException

offset

Error message

offset

What it means

Guard in HMACMD5.ComputeHash: the 'offset' argument (start position in the input buffer) was negative or greater than the buffer length, so no valid slice of the buffer can be hashed; ArgumentOutOfRangeException is thrown before hashing.

Solutions

1. Validate 0 <= offset <= buffer.Length before the call
2. Reset the running offset when starting a new hash computation
3. Catch ArgumentOutOfRangeException and log buffer length vs offset

Example fix

// before
hmac.ComputeHash(buf, pos, buf.Length - pos); // pos may exceed buf.Length
// after
if (pos >= 0 && pos <= buf.Length)
	hmac.ComputeHash(buf, pos, buf.Length - pos);

if (offset < 0 || offset > buffer.Length) throw new ArgumentException("offset out of bounds");

try { hmac.ComputeHash(buf, off, cnt); } catch (ArgumentOutOfRangeException ex) when (ex.ParamName == "offset") { /* reset offset */ }

When it happens

Trigger: Passing a negative offset or one beyond the end of the buffer, e.g. offsets carried over from previous chunked hashing.

Common situations: Streaming NTLM message signing where a running offset overruns the accumulated buffer.

Related errors

• count
• ArgumentOutOfRangeException
• No hash value computed.
• value
• buffer

AI-assisted analysis of jstedfast/MailKit@9d3859a785 (2026-09-15). Data as JSON: /api/errors/9409b5dc409e2755. Report an issue: GitHub.

Appendix: source

Thrown at MailKit/Security/Ntlm/HMACMD5.cs:106

		}

		public void Initialize ()
		{
			hash.Init (new KeyParameter (Key));
		}

		public void Clear ()
		{
			Dispose (false);
		}

		public byte[] ComputeHash (byte[] buffer, int offset, int count)
		{
			if (buffer == null)
				throw new ArgumentNullException (nameof (buffer));

			if (offset < 0 || offset > buffer.Length)
				throw new ArgumentOutOfRangeException (nameof (offset));

			if (count < 0 || offset > buffer.Length - count)
				throw new ArgumentOutOfRangeException (nameof (count));

			if (disposed)
				throw new ObjectDisposedException ("HashAlgorithm");

			HashCore (buffer, offset, count);
			hashValue = HashFinal ();

			return hashValue;
		}

		public byte[] ComputeHash (byte[] buffer)
		{
			if (buffer == null)
				throw new ArgumentNullException (nameof (buffer));

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