CVE-2026-55166
CRITICALDescription
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.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L
Exploit Intelligence
Low risk: more likely to be exploited than 12% of all known CVEs.
References
Related Vulnerabilities
Other CWE-285 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-29927 | Critical | 9.1 | 99% | - | Fix |
| CVE-2023-32707 | High | 8.8 | 79% | - | Fix |
| CVE-2021-28799 | Critical | 10.0 | 78% | KEV + Ransom | Fix |
| CVE-2023-48241 | High | 7.5 | 73% | - | Fix |
| CVE-2023-22480 | High | 7.3 | 67% | - | Fix |
| CVE-2022-3229 | Critical | 9.8 | 66% | - | - |
Common questions
How do I fix CVE-2026-55166?
No published fix for CVE-2026-55166 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-55166 being actively exploited?
Not that we know of. CVE-2026-55166 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.22% is the estimated probability that it will be exploited in the next 30 days. That is higher than 12% of all scored CVEs.
How severe is CVE-2026-55166?
CVE-2026-55166 has a CVSS v3 base score of 9.9, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-18.