Out-of-Bounds Read in github.com/gomarkdown/markdown (CVE-2026-102941)
Summary
Vulnerability in github.com/gomarkdown/markdown (CVE-2026-102941). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 0.0.0-20260724235538-61af6e1e6971 or later.
Original description
The description as published by the source.
Summary
IsSafeURL slices url[:nPath] before checking that len(url) >= nPath, so a URL shorter than a path prefix (0, 1 or 2 bytes) triggers a slice-bounds panic, and this is reached end to end when the html.Safelink hardening flag is enabled and the input contains an empty or very short link destination, giving an unrecoverable crash DoS. Confirmed at HEAD (e08cff8; present since 2022).
The defect
parser/parser.go, IsSafeURL:
func IsSafeURL(url []byte) bool {
nLink := len(url)
for _, path := range validPaths { // "/", "./", "../"
nPath := len(path)
linkPrefix := url[:nPath] // line 789: sliced BEFORE the length guard
if nLink >= nPath && bytes.Equal(linkPrefix, path) { // line 790: guard is too late
...
url[:nPath] is evaluated before the nLink >= nPath check. When len(url) < nPath and cap(url) < nPath, the slice expression panics. Only the relative-path loop is affected; the adjacent URIs loop is already correctly guarded (the signal that this one deviates, the same signal as the anchor). Input: IsSafeURL("") panics ([:1] cap 0), IsSafeURL(".") panics ([:2] cap 1), IsSafeURL("..") panics ([:3] cap 2), while IsSafeURL("/") returns true. End to end: markdown.ToHTML(input, html.CommonFlags|html.Safelink) with input [x]() panics. Attacker model: (1) any service rendering untrusted Markdown with the html.Safelink flag (the URL-sanitizing hardening flag itself introduces the crash); or…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-102941 has been found in github.com/gomarkdown/markdown.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade github.com/gomarkdown/markdown to 0.0.0-20260724235538-61af6e1e6971 or later.
If unsure, ask your IT team or search "github.com/gomarkdown/markdown CVE-2026-102941" on the vendor's site.
CVE-2026-102941 (github.com/gomarkdown/markdown) — CWE-125 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 0.0.0-20260724235538-61af6e1e6971 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Out-of-bounds read (CWE-125) exists in github.com/gomarkdown/markdown.
Check the vendor advisory for the affected versions of github.com/gomarkdown/markdown.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 0.0.0-20260724235538-61af6e1e6971.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/gomarkdown/markdown' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'github.com/gomarkdown/markdown' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
github.com/gomarkdown/markdownを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade github.com/gomarkdown/markdown to 0.0.0-20260724235538-61af6e1e6971ステージング環境で 0.0.0-20260724235538-61af6e1e6971 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。