CVE-2026-55166 Lemur: ACME SSRF + creator-equality IDOR lead to AWS IAM/PKI compromise
Authenticated users can exploit SSRF in ACME URL handling to steal cloud credentials and access private keys via IDOR.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55166?
CVE-2026-55166 is a critical server-side request forgery vulnerability in Netflix lemur, published on 18 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-55166?
3 open source packages ship an affected version, including lemur.
| Package | Affected | Fixed in |
|---|---|---|
lemur PyPI | All versions | 1.9.2 |
lemur PyPI | All versions | 1.9.2 |
lemur PyPI | All versions | 1.9.2 |
How do I fix CVE-2026-55166?
Upgrade lemur to 1.9.2 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-55166 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55166 exists.
Sources
Also known as GHSA-v2wp-frmc-5q3v, PYSEC-2026-384.