Summary
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()
}
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].
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.
Impact
Process crash, no auth, no preconditions. Same severity tier as the two May 13 advisories on this file.
CVE-2026-62866 has a CVSS score of 6.2 (Medium). The vector is requires local access, 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. A fixed version is available (3.11.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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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] == '/' {
Frequently Asked Questions
- What is CVE-2026-62866? CVE-2026-62866 is a medium-severity security vulnerability in github.com/tomwright/dasel/v3 (go), affecting versions >= 3.0.0, < 3.11.2. It is fixed in 3.11.2.
- How severe is CVE-2026-62866? CVE-2026-62866 has a CVSS score of 6.2 (Medium). 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.
- Which versions of github.com/tomwright/dasel/v3 are affected by CVE-2026-62866? github.com/tomwright/dasel/v3 (go) versions >= 3.0.0, < 3.11.2 is affected.
- Is there a fix for CVE-2026-62866? Yes. CVE-2026-62866 is fixed in 3.11.2. Upgrade to this version or later.
- Is CVE-2026-62866 exploitable, and should I be worried? Whether CVE-2026-62866 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
- What actually determines whether CVE-2026-62866 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.
- How do I fix CVE-2026-62866? Upgrade
github.com/tomwright/dasel/v3to 3.11.2 or later.