Two CVSS 10.0 Vulnerabilities: Zero-Click Email RCE and JWT Auth Bypass Require Immediate Action
The Two Highest-Priority Patches Today
Two perfect-10 vulnerabilities dropped with patches available. Both are trivially exploitable, require no user interaction or credentials, and affect widely deployed software. Treat these as emergency patch items.
FreeScout CVE-2026-28289: Email In, Web Shell Out
OX Security researchers discovered that FreeScout ≤1.8.206 — an open-source helpdesk platform — is vulnerable to unauthenticated remote code execution triggered entirely by receiving an email. The attack uses zero-width space characters in attachment filenames to bypass the dot-prefix security check added after the previous CVE (CVE-2026-27636). The filename [ZWSP].htaccess passes validation, then resolves to .htaccess after sanitization strips invisible characters — a textbook TOCTOU (time-of-check to time-of-use) flaw.
An attacker sends one email. FreeScout processes it automatically. A web shell is deployed. No click, no login, no exploit chain — just email delivery.
Per Shodan, over 1,100 FreeScout instances are internet-exposed. If you operate one and it's unpatched, treat it as compromised until verified clean. Upgrade to v1.8.207+ immediately and disable AllowOverrideAll in Apache configurations as a defense-in-depth measure.
pac4j-jwt CVE-2026-29000: Public Key = Full Auth Bypass
A critical algorithm confusion vulnerability in the pac4j-jwt library allows attackers to forge valid JSON Web Tokens using only the application's public key. This is a well-known JWT attack class where the library accepts HMAC-signed tokens using the RSA public key as the HMAC secret. Since public keys are, by definition, public — authentication is effectively non-existent for any application using this library.
pac4j-jwt is embedded across Java/JVM ecosystems and may be a transitive dependency buried several layers deep in your application stack. Run SBOM and SCA scans across all JVM applications immediately. Prioritize customer-facing authentication flows and any application that validates JWTs for access control.
Why These Two Matter Together
These aren't just high-severity bugs — they represent two of the most dangerous vulnerability classes in one advisory cycle: zero-interaction remote code execution and authentication bypass requiring no secrets. Neither requires an exploit chain. Neither requires social engineering. Both are patchable today.
| Dimension | FreeScout CVE-2026-28289 | pac4j-jwt CVE-2026-29000 |
|---|---|---|
| CVSS | 10.0 | 10.0 |
| Attack Vector | Email (zero-click) | Network (forged JWT) |
| Authentication Required | None | None (public key only) |
| User Interaction | None | None |
| Impact | Full RCE via web shell | Complete auth bypass |
| Detection | Shodan/Censys for exposure | SBOM/SCA for dependency |
| Fix Available | v1.8.207+ | Latest pac4j-jwt release |
What to do
Patch all FreeScout instances to v1.8.207+ and disable AllowOverrideAll in Apache configs. Run Shodan/Censys scans for any instances your asset inventory missed.
Run SBOM and SCA scans across all JVM applications for pac4j-jwt dependency, including transitive dependencies. Prioritize customer-facing and auth-critical applications.
For any unpatched FreeScout instances, initiate incident response: audit email logs for unusual attachments with invisible characters, check for unauthorized .htaccess files and web shells.