CVE-2026-53531

### Summary RaTeX’s recursive-descent parser recurses one (or more) native stack frame per nesting level at `{`, `\left`, `\sqrt{`, `^{`, etc, with **no maximum depth limit**. A short, ~10 KB input of nested groups overflows the 8 MB main-thread stack and aborts the process. With `panic = "abort"` (`Cargo.toml:48`), and because a Rust stack overflow is always a fatal `SIGABRT` regardless of panic strategy this is an unrecoverable, whole-process denial of service reachable from a single untrusted LaTeX string. ### Details The mutual recursion has no depth guard (`crates/ratex-parser/src/parser.rs`): ``` parse_expression (:113) -> parse_atom (:281/285) -> parse_group (:451) ^ | | on '{' (:459) recurse | +--------------------------+ ``` `\left` adds another recursive edge: `handle_left` → `parse_expression` (`crates/ratex-parser/src/functions/left_right.rs:47`). The only counters present are unrelated to depth: `leftright_depth` (a `\right`-matching counter, `parser.rs:24`) and the macro expander’s `max_expand = 1000` (`macro_expander.rs:64`), which does **not** gate brace / `\left` recursion (those tokens never pass through `expand_once`). There is no `recursion_limit`/depth parameter on `parse_group`, `parse_expression`, or `parse_atom`. ### PoC <img width="1097" height="158" alt="image" src="https://github.com/user-attachments/assets/29b837a2-c455-4cb6-a055-514b31c999c6" /> ``` $ python3 -c 'import sys;sys.stdout.write("{"*200000+"x"+"}"*200000)' | ./target/release/parse thread 'main' has overflowed its stack fatal runtime error: stack overflow, aborting Aborted (core dumped) # exit 134 ``` (Other nesting forms work equally, e.g. `\left(`×N, `\sqrt{`×N, `^{`×N.) ### Impact A single small request crashes the whole RaTeX process. In a typical server-side math-rendering service this is a reliable, unauthenticated