SSL-VPN Tunnel Disconnects with Signal 11 in sslvpnd during SAML 2.0 Auth
Remote access SSL-VPN worker process /bin/sslvpnd crashes with signal 11 (SIGSEGV) in saml_process_assertion+0x84 when enterprise users authenticate via SAML 2.0 Identity Providers sending large multi-valued group attribute claims, abruptly terminating all active user tunnels.
Technical Root Cause Analysis
When FortiGate authenticates SSL-VPN users via SAML 2.0 identity providers (Azure AD / Microsoft Entra ID, Okta, PingFederate), the client browser posts a base64-encoded XML SAMLResponse assertion to the SSL-VPN web portal endpoint.
The user-space daemon sslvpnd invokes saml_process_assertion() to extract user attributes and group claims for firewall policy group matching. In affected builds, the routine allocates a fixed-length buffer of 4096 bytes to process incoming <Attribute Name="http://schemas.microsoft.com/ws/2008/06/identity/claims/groups"> tags. When an enterprise employee belongs to dozens or hundreds of corporate directory groups, the concatenated claim strings exceed the buffer boundary. This triggers an invalid pointer dereference at offset +0x84, raising a SIGSEGV (signal 11) kernel trap that immediately kills the worker process and severs all concurrent tunnels served by that worker.
Affected Firmware & Blast Radius Matrix
| FortiOS Branch | Vulnerable Builds | Confirmed Clean Build | Status & Workaround |
|---|---|---|---|
| FortiOS 7.2 | 7.2.3 – 7.2.6 | 7.2.7+ | Filter SAML group claims at IdP portal |
| FortiOS 7.4 | 7.4.0 – 7.4.2 | 7.4.3+ | Upgrade recommended or emit assigned groups only |
| FortiOS 7.0 | Not Affected | 7.0 Branch Clean | Legacy SAML XML parser handles token boundaries |
Platform Impact: High-impact across FortiGate 100F, 200F, 400F, and 600F appliances serving enterprise remote worker populations with SAML 2.0 MFA authentication.
Step 01: Free Verification CLI (Safe Read-Only)
Execute these diagnostic commands to confirm whether your FortiGate has experienced sslvpnd worker crashes and monitor live SAML authentication debugging:
Diagnostic Commands
# 1. Read crashlog to identify sslvpnd signal 11 crash events and timestamps
diagnose debug crashlog read | grep sslvpnd
# 2. Check active SSL-VPN daemon processes and child worker PIDs
diagnose sys process pidof sslvpnd
# 3. View currently connected SSL-VPN users and tunnel uptime
diagnose vpn ssl list
# 4. Enable non-intrusive real-time SAML daemon trace
diagnose debug application samld -1
diagnose debug enableRemediation & Workaround Steps (Teaser Preview)
Follow the complete step-by-step remediation guide in the Ferrite interactive platform:
Frequently Asked Questions
When a remote user authenticates via SAML 2.0, the IdP sends a signed XML assertion containing user attributes and group memberships. In affected FortiOS builds, saml_process_assertion+0x84 allocates a fixed-size stack buffer to parse multi-valued group claims. If a user belongs to dozens of enterprise groups, the buffer overflows, corrupting adjacent pointer registers and causing an immediate Linux SIGSEGV.
The sslvpnd daemon operates a master/worker process architecture where a worker process manages an entire pool of tunnel endpoints. When the worker crashes on signal 11, the operating system tears down all network sockets associated with that PID, immediately terminating hundreds of established client connections.
Modify the enterprise application claim rules in Azure AD / Entra ID or Okta to emit only groups assigned to the application, or customize the group claim filter regex to prevent massive multi-valued XML arrays from reaching the FortiGate.