ratex-parser panics on \verb with a multibyte delimiter (UTF-8 byte-boundary slice)
Summary
The public parser entrypoint ratex_parser::parse(&str) panics on the 9-byte input \verbéxé (i.e. \verb followed by the non-ASCII delimiter é). When handling a \verb command, the parser slices the verbatim argument with byte indices (arg[1..arg.len() - 1]); if the delimiter character is multibyte UTF-8, index 1 lands inside that character and Rust panics with *“byte index 1 is not a char boundary”*. Because RaTeX’s release profile sets panic = "abort" (Cargo.toml:48), the panic aborts the entire process — not just the current request/thread — making this a hard denial of service for any service that renders untrusted LaTeX.
Details
Affected code
crates/ratex-parser/src/parser.rs, parse_symbol_inner:
```rust
if let Some(stripped) = text.strip_prefix("\\verb") { // parser.rs:901
self.consume();
let arg = stripped.to_string(); // e.g. "éxé"
let star = arg.starts_with('*');
let arg = if star { &arg[1..] } else { &arg }; // parser.rs:905 (also byte-sliced)
if arg.len() < 2 { // byte length
return Err(ParseError::new("\\verb assertion failed", Some(&nucleus)));
}
let body = arg[1..arg.len() - 1].to_string(); // parser.rs:910 <-- PANIC on multibyte delimiter
...
}
```
For input \verbéxé: arg = "éxé", where é = U+00E9 (bytes C3 A9). arg.len() is the byte length (5), the < 2 guard passes, and arg[1..4] starts at byte index 1 — inside the first é (bytes 0..2) — so the slice panics. The lexer groups \verb<delim>…<delim> correctly with char semantics (lexer.rs lex_verb); only the parser mishandles it.
PoC
<img width="1109" height="205" alt="image" src="https://github.com/user-attachments/assets/cd4bc6ae-23dd-458f-826c-6ce4e85c7005" />
```
$ printf '\\verb\xc3\xa9x\xc3\xa9\n' | ./target/release/parse
thread 'main' panicked at crates/ratex-parser/src/parser.rs:910:27:
start byte index 1 is not a char boundary; it is inside 'é' (bytes 0..2 of string)
Aborted (core dumped) # exit 134 — panic=abort kills the whole process
```
Impact
Any application that renders untrusted LaTeX through RaTeX (web “render this math” endpoint, WASM in-browser use, the FFI embedded in another app) can be crashed by a tiny string. With panic = "abort" in release builds, the crash takes down the whole process / server, so a single malicious formula causes a full-service DoS (and, in batch pipelines, drops all queued work).
Remediation
Slice by character boundaries instead of byte indices, mirroring the UTF-8-correct logic the lexer already uses. For example:
```rust
let chars: Vec<char> = arg.chars().collect();
if chars.len() < 2 { return Err(ParseError::new("\\verb assertion failed", Some(&nucleus))); }
let body: String = chars[1..chars.len() - 1].iter().collect();
```
(Apply the same char-aware handling to the * strip at parser.rs:905.) More broadly, consider not using panic = "abort" for builds embedded in long-running services, and/or wrapping parsing in catch_unwind at the FFI/WASM boundary — but the byte-slice fix is the direct correction.
