HTTPS interception

In an advisory sent to enterprises across the US, the Department of Homeland Security’s US-CERT group is warning that security products which perform HTTPS interception might weaken a company's overall security.

HTTPS inspection is a method where security products set up a man-in-the-middle proxy for HTTPS traffic. The proxy stands between the client and the remote server and intercepts HTTPS traffic, inspecting it for malware, and rebuilding the connection.

The issue comes from the fact that many security products, such as firewalls or antivirus products, fail to reconstruct the SSL connections to the same standards clients and servers negotiated.

"Many HTTPS inspection products do not properly verify the certificate chain of the server before re-encrypting and forwarding client data, allowing the possibility of a MiTM attack," US-CERT wrote in its advisory. "Furthermore, certificate-chain verification errors are infrequently forwarded to the client, leading a client to believe that operations were performed as intended with the correct server."

Research paper triggered CERT warning

The CERT advisory came after a group of security experts published a research paper at the start of the month titled "The Security Impact of HTTPS Interception."

The research team, made up of experts from Google, Mozilla, Cloudflare, and the University of Michigan, showed that around 62% of the HTTPS connections they've studied featured "reduced security," while 58% contained "severe vulnerabilities."

"We investigated popular antivirus and corporate proxies, finding that nearly all reduce connection security and that many introduce
vulnerabilities (e.g., fail to validate certificates)," the researchers concluded in their paper.

"While the security community has long known that security products intercept connections, we have largely ignored the issue, believing that only a small fraction of connections are affected. However, we find that interception has become startlingly widespread and with worrying consequences."

Will Dormann, a vulnerability analyst for US-CERT has also published a blog post detailing the dangers of improper HTTPS interception, and highlighted possible issues such as:

Incomplete validation of upstream certificate validity
Not conveying validation of upstream certificate to the client
Overloading of certificate Canonical Name (CN) field
Use of the application layer to convey certificate validity
Use of a User-Agent HTTP header to determine when to validate a certificate
Communication before warning
Same root CA certificate

Companies that want to test if their HTTPS inspection tools weaken HTTPS security can do so by using the BadSSL service.

Dormann also published a list of security products that perform HTTPS interception and may be possibly affected.

    A10 vThunder
    Arbor Networks Pravail
    Baracuda Web Filter
    BASCOM School Web Filter
    Bloxx Web Filter
    Blue Coat SSL Visibility Appliance
    Check Point Data Loss Prevention (DLP), Anti Virus, Anti-Bot, Application Control, URL Filtering, Threat Emulation and IPS.
    Cisco ScanCenter
    Citrix NetScaler AppFirewall
    Clearswift SECURE Web Gateway
    ContentKeeper
    Cymphonix Internet Management Suite
    Dell SonicWALL
    EdgeWave iPrism Web Security
    ESET Smart Security
    F5 BIG-IP
    Fortinet FortiGate
    Fidelis Security XPS
    Finjan Vital Security
    GFI WebMonitor
    GigaMon GigaSmart
    IBM Security Network Protection
    iboss Web Security
    iSHERIFF Cloud Security
    Juniper IDP devices
    Kaspersky Anti-Virus
    Komodia SSL Decoder
    M86 Secure Web Gatewayr
    McAfee Web Gateway and Firewall Enterpriser
    Microsoft Forefront TMG
    NetNanny
    NextGig Netronome
    Optenet WebFilter
    Palo Alto PAN-OS
    Panda Cloud Internet Protection
    PrivDog
    Radware AppXcel
    SafeNet eSafe Web Security Gateway
    Sangfor IAM
    Smoothwall Secure Web Gateway
    Sophos Cyberoam
    Sourcefire SSL Appliance
    Squid
    Symantec Web Gateway
    Thomason Technologies Next Gen IPS
    Trend Micro Deep Security
    Trustwave WebMarshal, Secure Web Gateway
    Untangle NG Firewall
    Venafi TrustAuthority
    VSS Monitoring vInspector
    WatchGuard HTTPS Proxy
    Wavecrest CyBlock
    WebSense Content Gateway
    WebTitan
    Qbik WinGate
    WolfSSL SSL Inspection
    Zscaler
    ZyXel Firewall