[Low] Arbitrary C code injection via unsanitized invariant pointer symbols in generated fuzzer.c

[donjon-cerberus-sandbox]

Location

• File: src/cgen/emit.zig
• Lines: 278-282

Classification

Property	Value
Severity	High
Category	Other
CWE	CWE-CWE-94
OWASP	A03:2021-Injection
Confidence	Suspected
Likelihood	Medium

Technical Description

Pointer target names from invariants are treated as trusted identifiers and emitted verbatim into generated C code. Invariant.applyToGlobals collects unknown .pointers targets from the attacker-controlled .zon invariant and stores them in func_symbols; emit.writeFuzzerC then interpolates each raw string into an extern declaration, and emitDomainTables later emits &<symbol> initializers for the same names. Because these strings are not validated as C identifiers, a crafted invariant can inject arbitrary C syntax into fuzzer.c. In workflows that automatically generate and compile the emitted fuzzer, this becomes build-time code injection and can lead to arbitrary code execution on the build host.

Vulnerable Code

for (func_symbols) |sym| {
    const func_decl = try std.fmt.allocPrint(allocator, "extern void {s}(void);\n", .{sym});
    defer allocator.free(func_decl);
    try file.writeAll(func_decl);
}

Impact

User input: attacker who can provide or modify the .zon invariant file can inject arbitrary C code into generated output, which may execute in CI/build systems when fuzzer.c is compiled or when the resulting binary is run. This can compromise developer workstations or build runners and poison generated fuzzing artifacts.

Remediation

Treat invariant pointer names as untrusted input. Before storing or emitting them, require them to match a strict C identifier pattern (^[A-Za-z_][A-Za-z0-9_]*$). Reject invariants containing invalid symbol names instead of interpolating raw strings into C templates.

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Created by Cerberus Merlin

[0pendev]

This is a known behavior.
An attacker would need access to the invariant declaration.
It will then be able to gain code execution in a fuzzer.

IMO, not a HIGH severity given what absolution is used for.
Still could be interesting to check if we can fix this without being to resource heavy.