🤖 Overview

The sslbot is a legitimate web crawler operated by Qualys, Inc., specifically as part of the Qualys SSL Labs service (formerly known as SSL Labs), which provides free SSL/TLS configuration testing and certificate analysis. Its primary purpose is to automatically scan public web servers to assess SSL/TLS deployment quality, certificate trust chain validity, and susceptibility to known vulnerabilities like Heartbleed or POODLE. The data feeds into the widely-used SSL Server Test and the Certificate Transparency monitoring system.

🌐 Technical Behavior

The sslbot performs TCP port 443 connections and TLS handshakes, requesting the root path (/) and optionally /favicon.ico or other endpoints to gather certificate data. According to official Qualys documentation, it sends requests from IP addresses within Qualys’s own ASN (ASN 13808), typically ranging from 64.39.96.0/20 and 199.47.80.0/20. Requests are made at irregular intervals, often every 24 hours or on-demand via the SSL Labs API. The bot uses HTTP/1.1 and may include a Host header; it does not alter HTTP methods beyond GET. It respects Connection: close and does not retain session cookies. The crawl pattern is deterministic: it connects, completes a TLS handshake, retrieves the certificate, and immediately closes the connection without parsing page content.

📋 robots.txt Compliance

According to the SSL Labs official documentation, the sslbot honors robots.txt directives by default. Specifically, it checks the /robots.txt file of the target domain and will skip scanning any path disallowed for User-agent: *. However, it does not obey per-path disallows that are not relevant to its function (e.g., it still probes port 443 regardless of file paths). Qualys states that administrators can block the bot entirely by adding Disallow: / for the user agent sslbot.

🔍 Detection Indicators

The primary User-Agent string is Mozilla/5.0 (compatible; sslbot/1.0; +https://www.ssllabs.com/projects/documentation/ssl-bot.html) as published on the official SSL Labs page. Some versions may use sslbot without a browser-like prefix. Behavioral fingerprints include: initiating a TLS handshake on port 443 with a single GET request to / or /favicon.ico; not requesting any other resources; having a connection duration under 5 seconds; and originating from Qualys IP ranges. The bot does not set identifiable custom HTTP headers beyond standard ones like Accept and Host.

📊 Data Usage

Collected data—namely server certificate details, cipher suite support, protocol versions, and handshake timing—is used to generate publicly accessible SSL/TLS security ratings (A+ through F) on the SSL Labs website. These results help system administrators and security researchers identify misconfigurations, expired certificates, or known vulnerabilities. The data is also aggregated into statistical reports on global SSL deployment trends and is used for the Certificate Transparency log monitoring project.

⚙️ Rate Limiting Policy

sslbots are rate-limited because they perform full TLS handshakes that can consume server resources, particularly on high-traffic domains. The rationale for threshold-based blocking is to prevent unintentional denial-of-service conditions: administrators are advised to limit sslbot to a maximum of one scan per domain per hour using firewall rules or robots.txt disallows if the bot’s behavior impacts production traffic.

ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the bots listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.