GHSA-77fj-vx54-gvh7 is a high-severity (CVSS 7.5) Out-of-bounds Read vulnerability in github.com/gomarkdown/markdown. A fix is available for github.com/gomarkdown/markdown — see the affected versions and patch details below.
Go Markdown has an Out-of-bounds Read in SmartypantsRenderer
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for GHSA-77fj-vx54-gvh7.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-77fj-vx54-gvh7 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/gomarkdown/markdownReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Processing a malformed input containing a < character that is not followed by a > character anywhere in the remaining text with a SmartypantsRenderer will lead to Out of Bounds read or a panic.
Details
The smartLeftAngle() function in html/smartypants.go:367-376 performs an out-of-bounds slice operation when processing a < character that is not followed by a > character anywhere in the remaining text.
https://github.com/gomarkdown/markdown/blob/37c66b85d6ab025ba67a73ba03b7f3ef55859cca/html/smartypants.go#L367-L376
If the length of the slice is lower than its capacity, this leads to an extra byte of data read. If the length equals the capacity, this leads to a panic.
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())
}
Impact
This vulnerability will lead to a Denial of Service / panic on the processing service.
-- The Datadog Security Team
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/gomarkdown/markdown | all versions | 0.0.0-20260411013819-759bbc3e3207go get github.com/gomarkdown/markdown@v0.0.0-20260411013819-759bbc3e3207 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/gomarkdown/markdown, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/gomarkdown/markdown to 0.0.0-20260411013819-759bbc3e3207 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-77fj-vx54-gvh7 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-77fj-vx54-gvh7 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-77fj-vx54-gvh7. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This is an Important denial of service flaw affecting Red Hat products that utilize the `github.com/gomarkdown/markdown` library. The vulnerability occurs when the `SmartypantsRenderer` processes specially crafted malformed Markdown input containing an unclosed '<' character, leading to an out-of-bounds read or…
| Product | Fixed in | Advisory |
|---|---|---|
| Multicluster Global Hub 1.4.9 | multicluster-globalhub/multicluster-globalhub-grafana-rhel9:1779579439 | RHSA-2026:22347 |
| Multicluster Global Hub 1.6.5 | multicluster-globalhub/multicluster-globalhub-grafana-rhel9:1780167118 | RHSA-2026:23345 |
| Multicluster Global Hub 1.7.3 | multicluster-globalhub/multicluster-globalhub-grafana-rhel9:1779925273 | RHSA-2026:24503 |
| Red Hat Advanced Cluster Management for Kubernetes 2.15 | rhacm2/acm-grafana-rhel9:1780677003 | RHSA-2026:24539 |
| Red Hat multicluster global hub 1.5.3 | multicluster-globalhub/multicluster-globalhub-grafana-rhel9:1778867753 | RHSA-2026:21769 |
Frequently Asked Questions
Is GHSA-77fj-vx54-gvh7 in your dependencies?
O3 Security finds GHSA-77fj-vx54-gvh7 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.