Detect CVE-2026-55166: Lemur ACME SSRF and IDOR Leading to AWS IAM/PKI Compromise in CrowdStrike LogScale
Detects exploitation of CVE-2026-55166 in Netflix Lemur (versions < 1.9.2), which combines an ACME protocol Server-Side Request Forgery (CWE-918) with a creator-equality Insecure Direct Object Reference (CWE-639/CWE-285). Successful exploitation allows an attacker to pivot from certificate management to AWS IAM credential theft and PKI infrastructure compromise. PoC is publicly available.
MITRE ATT&CK
LogScale Detection Query
#event_simpleName IN ("NetworkConnectIP4", "ProcessRollup2", "ScriptControlScanTelemetry")
| where
(
event_simpleName = "NetworkConnectIP4" and
(
RemoteIP IN ("169.254.169.254", "169.254.169.253") or
RemotePort IN (80, 8080, 443) and
(
RemoteIP startswith "169.254."
)
)
) or
(
event_simpleName = "ProcessRollup2" and
(
CommandLine matches regex "(curl|wget|python|requests).*169\.254\.169\.254" or
CommandLine matches regex "(curl|wget).*lemur.*api.*(certificate|authority)" or
CommandLine matches regex "acme.*--url.*http://(127\.|10\.|192\.168\.|172\.1[6-9]\.|172\.2[0-9]\.|172\.3[01]\.)"
)
)
| eval attack_type = case(
RemoteIP = "169.254.169.254", "AWS_METADATA_SSRF",
CommandLine matches regex "acme.*--url", "ACME_SSRF_CLI",
CommandLine matches regex "certificate.*[0-9]+", "IDOR_CERT_ENUM",
true(), "SUSPICIOUS_LEMUR_ACTIVITY"
)
| stats count() as event_count, values(CommandLine) as commands, values(RemoteIP) as remote_ips by aid, ComputerName, UserName, attack_type
| where event_count > 0
| sort - event_countCrowdStrike Falcon query detecting network connections to cloud metadata endpoints and process executions consistent with Lemur SSRF exploitation or IDOR certificate enumeration via CLI tools.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate AWS SDK calls from Lemur host reaching IMDS for IAM role credentials
- Authorized internal tooling using curl/wget for certificate API testing
- Cloud-native health check scripts that access instance metadata
- Security tooling performing SSRF discovery as part of authorized pentests
Other platforms for CVE-2026-55166
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1CVE-2026-55166 ACME SSRF via HTTP-01 Challenge URL Injection
Expected signal: Outbound HTTP GET to 169.254.169.254 from Lemur process; web log entry for POST /api/v1/certificates with pluginOptions containing acme_challenge_url
- Test 2CVE-2026-55166 IDOR Certificate Enumeration via Sequential ID Access
Expected signal: 200 HTTP responses to GET /api/v1/certificates/[1-200] from a single source IP; Lemur audit log entries for cross-user certificate access
- Test 3CVE-2026-55166 Chained SSRF + IDOR for AWS IAM Credential Harvest
Expected signal: Sequential GET requests to /api/v1/authorities/[1-50]; POST to /api/v1/certificates with IMDS URL in pluginOptions; outbound TCP connection from Lemur process to 169.254.169.254:80
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Get the full detection package for CVE-2026-55166 including response playbook, investigation guide, and atomic red team tests.