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SSL Blacklist (SSLBL) is a free abuse.ch threat-intelligence service that publishes SHA1 fingerprints of certificates associated with botnet command-and-control (C2) servers, along with other indicators defenders can use to detect related activity. It is not a certificate authority and does not decide whether a normal website certificate is valid or trustworthy. A fingerprint match is a lead to investigate—not proof that a particular device or endpoint is infected.
What SSLBL’s certificate blacklist tells you
SSLBL tracks certificates observed in connection with malicious infrastructure, especially botnet C2 servers. Its certificate CSV identifies each entry with a UTC listing date, a SHA1 fingerprint, and a reason for listing. Security teams can process those records for enrichment or SIEM searches; the listing is an indicator of association with malicious activity, not a universal verdict on every use of the certificate.
This is different from ordinary certificate validation. A browser’s certificate checks concern matters such as whether a connection’s certificate chains to a trusted authority and matches the requested site. SSLBL instead provides threat intelligence about certificates observed in a malware context. The two checks answer different questions: a validly issued certificate can still be associated with malicious infrastructure, and an SSLBL match alone does not establish that a specific endpoint is compromised.
SSLBL is operated by abuse.ch. Its data is offered for commercial and non-commercial use under CC0, while the project describes availability as “as it is on best effort.” Consult the current SSLBL About page and blacklist documentation for the service’s scope, formats, and terms.
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Choose a feed for the signal you need
SSLBL publishes several distinct indicator types. They observe different parts of network activity, so one feed is not a substitute for another.
| Feed | What it represents | Best fit and cautions |
|---|---|---|
| Certificate CSV | SHA1 certificate fingerprints, UTC listing date, and listing reason | Processing, enrichment, or SIEM searches for certificate matches. |
| Suricata certificate rules | Network rules that detect or block connections based on certificate fingerprints | Choose the ruleset compatible with the installed Suricata version; do not load both certificate-rule alternatives. |
| C2 IP CSV or rules | Destination IP and port associations for servers using listed certificates | Network detection with Snort or Suricata. The ordinary IP list is limited to addresses seen with a malicious certificate in the previous 30 days to reduce problems from IP reassignment. |
| DNS Response Policy Zone (RPZ) | DNS policy entries associated with IPs running listed certificates | Resolver-based handling; depending on configuration, matching domains may be blocked, sinkholed, or logged. |
| JA3 CSV or rules | TLS client fingerprints associated with malware | Client-behavior detection, but SSLBL warns that the collection has not been tested against known-good traffic and may produce significant false positives. |
Feed formats, compatibility notes, and current download details are documented on the SSLBL Blacklist page.
Rank #2
Deploying the data and rules
For certificate searches or SIEM enrichment
Use the certificate CSV when your workflow can compare SHA1 fingerprints from observed TLS certificates against SSLBL’s entries. Retain the listing date and reason with a match so analysts can judge its context. A match should prompt review of surrounding telemetry—such as destination, time, process, and related alerts—rather than an automatic conclusion that a particular host is infected.
For Suricata certificate detection
The certificate-rules documentation lists one ruleset for Suricata 1.4 or newer and an alternative requiring Suricata 4.1.0 or newer. Select the alternative appropriate to the installed version; SSLBL says not to use both certificate rulesets at once.
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For C2 IP detection
The C2 IP ruleset supports both Suricata and Snort. Prefer the ordinary, recent IP list for routine monitoring: addresses can be reassigned, and SSLBL limits this list to IPs seen with a malicious certificate in the preceding 30 days. The project warns that the aggressive historical IP ruleset can generate false positives, so its broader history should not be treated as a more reliable version of the current list.
For DNS or client-fingerprint monitoring
Use DNS RPZ data when your resolver can apply policy to the associated domains, and choose whether matching queries should be blocked, sinkholed, or logged according to your environment. JA3 data represents TLS client behavior rather than a server certificate or destination IP; given SSLBL’s false-positive warning, validate matches against other evidence before taking action.
Rank #4
Keep feed refreshes within the documented cadence
SSLBL says its feeds and rulesets are generated every five minutes and asks consumers not to fetch them more frequently. Configure scheduled retrieval no faster than that interval, and check the project documentation for the supported format and deployment details for the feed you use.
How to interpret a match safely
- Confirm what matched. Distinguish a certificate fingerprint match from an IP, DNS, or JA3 match; they represent different observations.
- Preserve context. Record when and where the indicator was observed and correlate it with host, process, DNS, and network telemetry.
- Account for indicator age and reuse. An IP may later belong to another service; the ordinary C2 list’s 30-day window is relevant to that risk.
- Set response thresholds deliberately. Blocking may be appropriate in a managed environment, while an alert-and-investigate workflow may be safer where false positives carry high cost.
- Verify current entries before operational decisions. Feeds and rules change, and SSLBL serves data on a best-effort basis.
SSLBL’s displayed scale is a changing snapshot
On the SSLBL statistics page accessed October 4, 2026, it displayed 10,817 blacklisted SSL certificates, 97 blacklisted JA3 fingerprints, and 248 distinct malware families. AsyncRAT was listed as the top malware, and WE1 as the top issuing CA; SSLBL notes that the CA ranking includes self-signed certificates. These are volatile page totals and rankings, not annual counts or a measurement study. Check the live SSLBL statistics page for current values.
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