Detect CVE-2026-55166: Lemur ACME SSRF and IDOR Leading to AWS IAM/PKI Compromise in Sumo Logic CSE
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
Sumo Detection Query
_sourceCategory=web/access OR _sourceCategory=nginx OR _sourceCategory=haproxy
| parse "* * * [*] \"* * *\" * *" as src_ip, ident, user, time, method, uri, protocol, status, bytes nodrop
| if (isEmpty(uri), url, uri) as request_uri
| where request_uri matches "/api/v1/*"
| where (
(request_uri matches "*acme*" or request_uri matches "*challenge*" or request_uri matches "*validation*")
or request_uri matches "*169.254.169.254*"
or (method in ("GET","PUT","DELETE") and request_uri matches "/api/v1/certificates/*")
)
| eval attack_indicator = if(request_uri matches "*169.254.169.254*", "METADATA_SSRF",
if(request_uri matches "*acme*" and request_uri matches "*url=*", "ACME_SSRF",
if(request_uri matches "/api/v1/certificates/[0-9]*", "IDOR_ENUM", "UNKNOWN")))
| timeslice 5m
| stats count as hits, values(request_uri) as uris, values(attack_indicator) as indicators by src_ip, _timeslice
| where hits > 3 or indicators matches "*METADATA_SSRF*"
| sort by hits descSumo Logic query detecting Lemur exploitation patterns including ACME SSRF callback abuse, cloud metadata endpoint probing, and certificate IDOR enumeration from web access logs.
Data Sources
Required Tables
False Positives & Tuning
- Automated certificate management tools performing high-volume API operations
- Internal monitoring probing Lemur API endpoints for availability
- Authorized security testing generating ACME validation traffic
- Multi-tenant environments where different teams manage shared certificates
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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