Dasel: Selector lexer panics on trailing whitespace in `parseCurRune`

Same panic class as GHSA-m5j3-4634-c2vq and GHSA-m6xr-fvfg-5g64, sister site on the same function. Trigger is any selector ending in whitespace: dasel query 'a ' panics at selector/lexer/tokenize.go:60.

The whitespace-skip loop right above (lines 55-57) advances p.i to p.srcLen when the input is all-whitespace or whitespace-trailing. The very next line reads p.src[p.i] without a bounds check.

Vulnerable code

selector/lexer/tokenize.go:53-74 (v3.11.0):

func (p *Tokenizer) parseCurRune() (Token, error) {
	// Skip over whitespace
	for p.i < p.srcLen && unicode.IsSpace(rune(p.src[p.i])) {
		p.i++
	}

	// Skip over comments
	if p.src[p.i] == '/' && p.i+1 < p.srcLen && p.src[p.i+1] == '/' {
		// ...

Lines 69-71 right below already do the bounds check after the comment-skip path. The whitespace-only path slipped past it.

Reproduce

$ echo '{"a":1}' | dasel query -i json 'a '
panic: runtime error: index out of range [2] with length 2

goroutine 1 [running]:
github.com/tomwright/dasel/v3/selector/lexer.(*Tokenizer).parseCurRune(...)
	selector/lexer/tokenize.go:60
github.com/tomwright/dasel/v3/selector/lexer.(*Tokenizer).Next(...)
github.com/tomwright/dasel/v3/selector/lexer.(*Tokenizer).Tokenize(...)
github.com/tomwright/dasel/v3/selector.Parse(...)
github.com/tomwright/dasel/v3/execution.ExecuteSelector(...)

Other inputs that hit it: ' ', $'a\t', $'a\n', 'a ?? ', 'a + '. Any token (or no token) followed by whitespace.

Reachable directly from the library too - dasel.Query(ctx, input, "a ") panics the same way. Project-style test reproducer that fails on current main:

// drop into selector/lexer/ as tokenize_trailing_ws_test.go
package lexer_test

import (
	"testing"
	"github.com/tomwright/dasel/v3/selector/lexer"
)

func TestTokenize_TrailingWhitespacePanic(t *testing.T) {
	defer func() {
		if r := recover(); r != nil {
			t.Fatalf("Tokenize panicked: %v", r)
		}
	}()
	_, _ = lexer.NewTokenizer("a ").Tokenize()
}

Impact

Process crash, no auth, no preconditions. Same severity tier as the two May 13 advisories on this file.

Affected versions

All v3.x. The whitespace-skip loop was added in 78fcca9 (Dasel V3, ~9 months ago); line 60's indexing landed in 9bfe966 (~6 months ago). Reproduced on github.com/tomwright/dasel/[email protected].

Suggested fix

One line, between the whitespace-skip loop and the comment-skip access. Same shape as lines 69-71:

func (p *Tokenizer) parseCurRune() (Token, error) {
	for p.i < p.srcLen && unicode.IsSpace(rune(p.src[p.i])) {
		p.i++
	}

	if p.i >= p.srcLen {
		return NewToken(EOF, "", p.i, 0), nil
	}

	if p.src[p.i] == '/' && p.i+1 < p.srcLen && p.src[p.i+1] == '/' {

Prevalence

The other two cases in this class shipped fixes two weeks ago; this one wasn't covered in those patches. I checked the rest of parseCurRune for other unguarded direct-access points after a pos++ - nothing else stood out. A testing.F harness on lexer.NewTokenizer(s).Tokenize() catches all three with trivially short inputs and would close the class.