Dasel: Denial of service in dasel selector lexer due to infinite loop on unterminated regex literal

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Dasel is a command-line tool and library for querying, modifying, and transforming data structures. From 3.0.0 until 3.10.1, the selector lexer matchRegexPattern closure in (*Tokenizer).parseCurRune in selector/lexer/tokenize.go loops while tokenizing an unterminated regex literal such as r/ because peekRuneEqual returns false after the end of input, allowing attacker-controlled selector strings to consume CPU indefinitely. This issue is fixed in version 3.10.1.

Source published

16 Jul 2026 17:54:51 UTC

Source modified

17 Jul 2026 15:06:49 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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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 selector lexer matchRegexPattern closure in (*Tokenizer).parseCurRune in selector/lexer/tokenize.go loops while tokenizing an unterminated regex literal such as r/ because peekRuneEqual returns false after the end of input, allowing attacker-controlled selector strings to consume CPU indefinitely. 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 enters a non-terminating loop when tokenizing an unterminated regex pattern such as `r/abc`. A 2-byte input (`r/`) is sufficient to cause the tokenizer to consume 100% CPU on one core indefinitely. 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 `matchRegexPattern` closure within `(*Tokenizer).parseCurRune` in [`selector/lexer/tokenize.go#L237-L247`](https://github.com/TomWright/dasel/blob/fba653c7f248aff10f2b89fca93929b64707dfc8/selector/lexer/tokenize.go#L237-L247): ```go matchRegexPattern := func(pos int) *Token { if p.src[pos] != 'r' || !p.peekRuneEqual(pos+1, '/') { return nil } start := pos pos += 2 for !p.peekRuneEqual(pos, '/') { // line 243 pos++ } pos++ return ptr.To(NewToken(RegexPattern, p.src[start+2:pos-1], start, pos-start)) } ``` When no closing `/` exists, [`peekRuneEqual`](https://github.com/TomWright/dasel/blob/fba653c7f248aff10f2b89fca93929b64707dfc8/selector/lexer/tokenize.go#L39-L43) returns `false` when `pos >= srcLen` (because the bounds check at line 40 returns `false` for out-of-range positions). Since `!false = true`, the loop condition remains true and `pos` increments indefinitely. The function never returns. Notably, the same function already handles unterminated quoted strings by returning `UnexpectedEOFError`, but the regex pattern path does not perform a similar end-of-input check. Minimal trigger: `r/` (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" "time" "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{"r/unterminated", "r/"} { fmt.Printf("Input: %s\n", input) done := make(chan string, 1) go func() { t := lexer.NewTokenizer(input) start := time.Now() tokens, err := t.Tokenize() elapsed := time.Since(start) if err != nil { done <- fmt.Sprintf("Error after %v: %v", elapsed, err) } else { done <- fmt.Sprintf("OK after %v: %d tokens", elapsed, len(tokens)) } }() select { case result := <-done: fmt.Println(result) case <-time.After(5 * time.Second): fmt.Println("CONFIRMED: did not complete within 5s; tokenizer is stuck in non-terminating loop") } fmt.Println() } } ``` Observed output on `v3.3.1` in the test environment above: ```text Go version: go1.26.1 GOARCH: arm64 Input: r/unterminated CONFIRMED: did not complete within 5s; tokenizer is stuck in non-terminating loop Input: r/ CONFIRMED: did not complete within 5s; tokenizer is stuck in non-terminating loop ``` ### Impact An attacker who can control or influence the selector/query string passed to dasel can cause the tokenizer to enter a non-terminating loop. The affected process consumes 100% CPU on one core and does not make progress until externally terminated. 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 The regex scanner should bounds-check and return an error on unterminated regex literals, consistent with unterminated quoted strings. Since `matchRegexPattern` currently returns `*Token`, the fix also requires changing the function signature to propagate errors. For example: ```go matchRegexPattern := func(pos int) (*Token, error) { if p.src[pos] != 'r' || !p.peekRuneEqual(pos+1, '/') { return nil, nil } start := pos pos += 2 for pos < p.srcLen && p.src[pos] != '/' { pos++ } if pos >= p.srcLen { return nil, &UnexpectedEOFError{Pos: pos} } pos++ return ptr.To(NewToken(RegexPattern, p.src[start+2:pos-1], start, pos-start)), nil } ```

Source published

19 May 2026 20:09:20 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: Denial of service in dasel selector lexer due to infinite loop on unterminated regex literal in github.com/tomwright/dasel

Source published

25 Jun 2026 22:34:31 UTC

Source modified

25 Jun 2026 23:01:19 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.