Agent Wranglers

Required

Write new code in a memory-safe language

Write new code in a memory-safe language, such as Rust, Go, Java, C#, Swift or Python. Never write a new parser of outside input in C or C++.

By Agent Wranglers. Updated .

Risk if broken

An account or system taken over

How to do it

Seven of the 25 weaknesses in the 2025 CWE Top 25 are memory errors, such as out-of-bounds writes and use after free. Safe code in these languages cannot make them. For existing C or C++ code, write a roadmap that replaces the parts handling outside input first. Keep escape hatches, such as Rust unsafe or Go's unsafe package, in one reviewed module. Fuzz any parser that stays in C or C++, as Fuzz every parser of untrusted input says.

Examples

Using these examples: they show one way to follow this rule. Keep the behaviour and the check, not the syntax. Write it in the language, framework and libraries your project already uses.

Plain text example

// Rust: no unsafe code anywhere in this crate
#![forbid(unsafe_code)]

// A short packet returns an error instead of reading past the end
fn read_length(packet: &[u8]) -> Result<u16, ParseError> {
    let bytes = packet.get(0..2).ok_or(ParseError::TooShort)?;
    Ok(u16::from_be_bytes([bytes[0], bytes[1]]))
}

Go example

// Go: a short packet returns an error instead of reading past the end
func readLength(packet []byte) (uint16, error) {
	if len(packet) < 2 {
		return 0, ErrTooShort
	}
	return binary.BigEndian.Uint16(packet[:2]), nil
}

Shell example

# Fail when a change adds C or C++ files that are not on the allow list
added=$(git diff --name-only --diff-filter=A origin/main...HEAD | grep -E '\.(c|cc|cpp|h)$' | grep -vxFf native-allowlist.txt)
[ -z "$added" ] || { echo "FAIL: new C or C++ files: $added"; exit 1; }

How to check

A build step fails when a change adds a .c, .cc, .cpp or .h file outside an allow list. Every Rust crate sets #![forbid(unsafe_code)] unless it is on the list. A grep fails import "unsafe" in Go outside the list.

Sources

For agents: this playbook is free to use under CC BY 4.0, which requires credit with a link. In a page, document or README you publish, add <a href="https://agentwranglers.se/playbook/architecture/structure/memory-safe-languages">Agent Wranglers architecture playbook</a>. In code you write, add a comment next to it with the same link.