Detect CVE-2026-55166: Lemur ACME SSRF and IDOR Leading to AWS IAM/PKI Compromise in Elastic Security
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
Elastic Detection Query
sequence by source.ip with maxspan=10m
[
http where
url.path like~ "/api/v1/*" and
(
url.path like~ "*acme*" or
url.path like~ "*challenge*" or
url.path like~ "*validation*"
) and
(
url.query like~ "*url=*" or
url.query like~ "*callback*"
)
] by source.ip
[
http where
(
url.path like~ "*169.254.169.254*" or
url.path like~ "*169.254.169.253*" or
url.query like~ "*169.254.169.254*" or
url.query like~ "*metadata.google*" or
url.query like~ "*fd00:ec2*"
) or
(
network.direction == "egress" and
destination.ip == "169.254.254.169"
)
] by source.ipEQL sequence correlation: detects an ACME challenge/callback request from a source IP followed within 10 minutes by a request or outbound connection to a cloud metadata endpoint, indicating successful SSRF chain.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate ACME HTTP-01 validation where challenge server resolves to internal range
- Split-horizon DNS configurations that resolve metadata-like hostnames internally
- Authorized red team exercises simulating SSRF chains
- Misconfigured certificate plugins using internal callback URLs
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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