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CVE-2026-55166

Server-side request forgery (SSRF)

9.9 CRITICALEPSS 0.29%
  1. Published18 Aug 2026

Description

Lemur manages TLS certificate creation. Prior to 1.9.2, authenticated users could influence an ACME authority acme_url without an effective server-side destination restriction and trigger AcmeHandler.setup_acme_client to make backend requests. An attacker could target cloud instance metadata or internal services from Lemur network context, potentially obtaining credentials available to the host. The advisory also identifies creator-equality authorization behavior that could preserve access to certificate key material after ownership or role changes, with insufficient export_private_key audit context to distinguish that access path. Together, the acme_url server-side request forgery and authorization weakness could expose cloud credentials and long-lived PKI private-key access. The fix adds ACME_DIRECTORY_HOST_ALLOWLIST validation and enriches key-export audit events with creator and current-owner context. This issue is fixed in version 1.9.2.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredLow
User interactionNone
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityLow
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

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Frequently asked

Is CVE-2026-55166 being actively exploited?

CVE-2026-55166 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.29%.

How severe is CVE-2026-55166?

CVE-2026-55166 has a CVSS 3.1 base score of 9.9, rated critical. EPSS estimates a 0.29% probability of exploitation.

How do I fix CVE-2026-55166?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-55166 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.