VULNOS
All Threat Alerts
criticalCVE Alert
CVE-2026-73253

Critical Vulnerability: CVE-2026-73253 — cesanta — mongoose

Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() functions in src/tls_builtin.c call mg_match(), whose wildcard can cross DNS label boundaries, so a pattern such as *.example.com can match foo.bar.example.com. The resulting hostname verification bypass permits

Tuesday, September 29, 2026cesantaVulnios Threat Intelligence
Share:

Vulnerability Snapshot

CVE-2026-73253 is rated CRITICAL — exploitation is trivial or already observed in the wild and impact is severe. Patch immediately, not on the next maintenance window.

Affected technology: mongoose.

Executive Summary

Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() functions in src/tls_builtin.c call mg_match(), whose wildcard can cross DNS label boundaries, so a pattern such as *.example.com can match foo.bar.example.com. The resulting hostname verification bypass permits interception and modification of TLS traffic. This issue is fixed in version 7.22.

Why It Matters

CVE-2026-73253 is rated CRITICAL severity, requiring immediate attention from security teams.

CVSS Base Score: 9.1/10

Affected Technologies

Vendors: cesanta

Products: mongoose

🛡️What Defenders Should Check

  • Check if you are affected — Review your asset inventory for products listed in CVE-2026-73253.
  • Apply available patches — Visit vendor advisories for the latest security updates.
  • Monitor for exploitation — Check your SIEM/IDS logs for related indicators.

    • Use Vulnios to continuously monitor your exposure to CVE-2026-73253 and similar vulnerabilities.

    References & Sources

  • https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71
  • https://github.com/cesanta/mongoose/pull/3611
  • https://github.com/cesanta/mongoose/releases/tag/7.22
  • https://github.com/cesanta/mongoose/security/advisories/GHSA-jp6g-796f-39vp
  • https://github.com/cesanta/mongoose/security/advisories/GHSA-jp6g-796f-39vp

    • How Vulnios Detects This

    Vulnios scans for this vulnerability using Trivy and Grype for SBOM-based CVE matching and Vulnios CVE feed continuous monitoring against your asset inventory. Run a scan against your environment to see whether you are exposed; findings are linked back to the original CVE record so triage starts with the patch path already known.

    AI Security Advisor

    Powered by Gemini

    Get AI-powered security recommendations tailored to this specific threat — including risk assessment, detection guidance, MITRE ATT&CK mapping, and actionable remediation steps.

    Affected Products

    mongoose

    Sources

    Related Threat Alerts

    Frequently Asked Questions

    What is CVE-2026-73253?

    CVE-2026-73253 is a critical-severity vulnerability tracked under the Common Vulnerabilities and Exposures program. Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client

    Am I affected?

    Check whether your environment runs mongoose. If you operate any of those, treat yourself as in scope until you have evidence otherwise. A Vulnios scan will identify the exact assets carrying the affected version.

    How urgent is the response?

    Critical: do not wait for your normal patch cycle. Verify exposure today, apply the vendor patch immediately, and add detection rules for any post-exploit indicators.

    How do I remediate?

    Apply the vendor patch listed in the upstream advisory linked under Sources. If the patch is not yet available, follow the vendor-supplied workaround (often a config flag or feature disable) and add detections for the published exploit pattern in your SIEM. Re-scan after the patch lands to confirm the finding clears.

    Where can I track exploitation activity?

    Watch CISA's Known Exploited Vulnerabilities catalog for CVE-2026-73253. Cross-reference with public exploit databases and your own SIEM/IDS for indicator-of-compromise patterns. Vulnios tracks KEV status automatically and surfaces it on the asset findings view.

    How does Vulnios help with this?

    Vulnios continuously cross-references your asset inventory against the live CVE feed (NVD, vendor advisories, CISA KEV, and curated OSINT). When a new CVE matches your environment, you get a prioritized finding with the severity, KEV status, exploit-prediction (EPSS), and a direct path to the vendor patch. You can start a free scan from the homepage.

    critical

    Protect Your Organization

    Monitor CVEs, scan for vulnerabilities, and get real-time threat alerts — all in one platform.

    Get Started FreeFree Security ScanOSINT Dashboard

    Weekly threat digest

    KEV-listed exploits and vendor advisories, every Monday.

    One email a week. Unsubscribe any time.

    Get instant alerts on Telegram

    Join our public channel for real-time critical CVE alerts.

    Follow @vulnios