What is CVE-2026-55166?

CVE-2026-55166 is Lemur: any SSO-authenticated user achieves AWS IAM compromise and permanent PKI key access via ACME acme_url SSRF and creator-equality IDOR. The supplied enrichment data classifies it as SSRF mapped to CWE-285 CWE-285; CWE-639 CWE-639; CWE-918 Server-Side Request Forgery (SSRF).

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Active exploitation is not confirmed from current sources for CVE-2026-55166. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-55166 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

A public PoC is not confirmed from current sources for CVE-2026-55166. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS, cloud metadata access logs, egress proxy logs where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-55166 using CVSS 9.9, EPSS 0%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

Workarounds are not confirmed from current sources. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

criticalSSRF

CVE-2026-55166

CVE-2026-55166 — Lemur: any SSO-authenticated user achieves AWS IAM compromise and permanent PKI key access via ACME acme_url SSRF and creator-equality IDOR

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.

Published Aug 18, 2026Updated Aug 18, 2026Sources: NVD, Netflix (CNA), GitHub, GitHub Security Advisory, SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Unreported

no source claims exploitation

EPSS

ahead of 0% of scored CVEs

Affects

Netflix

2 products listed

CVSS base

9.9

critical

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

PoC

none · proof-of-concept · active

Automatable

can an attacker script all four kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

The vendor's own words where we have them.

Upgrade lemur to 1.9.2 or later (pip advisory GHSA-v2wp-frmc-5q3v).

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
Netflix	lemur	< 1.9.2	Vulnerable
pip	lemur	< 1.9.2	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Availability

Low

Confidentiality

High

Integrity

High

Scope

Changed

Attack Complexity

Low

Attack Vector

Network

Privileges Req

Low

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
9.9	CVSS 3.1	critical	3.1	6	GitHub (CNA), Netflix (CNA), GHSA

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L

What this weakness leads to

MITRE's own consequences and mitigations for the weakness class — the authority's wording, not guidance derived from the CVSS vector.

MITRE

CWE-285 · Improper Authorization

Read Application Data
Read Files or Directories
Modify Application Data
Modify Files or Directories

Mitigation: Divide the software into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.

CWE-639 · Authorization Bypass Through User-Controlled Key

Bypass Protection Mechanism
Gain Privileges or Assume Identity

Mitigation: For each and every data access, ensure that the user has sufficient privilege to access the record that is being requested.

Weakness & attack patterns

CWE-285
CWE-639
CWE-918Server-Side Request Forgery (SSRF)

Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.

CAPEC-13 · Subverting Environment Variable ValuesCAPEC-17 · Using Malicious FilesCAPEC-127 · Directory IndexingCAPEC-1 · Accessing Functionality Not Properly Constrained by ACLsCAPEC-104 · Cross Zone ScriptingCAPEC-77 · Manipulating User-Controlled VariablesCAPEC-5 · Blue BoxingCAPEC-87 · Forceful BrowsingCAPEC-647 · Collect Data from RegistriesCAPEC-51 · Poison Web Service RegistryCAPEC-59 · Session Credential Falsification through PredictionCAPEC-76 · Manipulating Web Input to File System Calls

T1574.010Hijack Execution Flow: ServicesFile Permissions Weakness
T1083File and Directory Discovery
T1562.003Impair Defenses: Impair Command History Logging

Social mentions

Posts naming this CVE. Attention, not evidence of exploitation — it spikes on disclosure and decays whether or not anything is exploited.

🚨 CRITICAL - Lemur ACME SSRF + private key authorization bypass chain (CVE-2026-55166) CVE-2026-55166 impacts Lemur’s ACME authority creation endpoint, which will fetch an attacker-supplied acme_url and can be abused to force outbound requests from the Lemur server. The root
@UpwindMDR· Jun 26, 2026

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Prioritize edge telemetry for network-reachable lemur.

web/proxy/WAF logsapplication logsnetwork IDS/IPScloud metadata access logsegress proxy logs

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 9.9 (AV:N)
Aug 18, 2026 · NVD
Initial · CVE published
Aug 18, 2026 · NVD
Added · GHSA-v2wp-frmc-5q3v published (critical)
Jun 25, 2026 · GitHub Security Advisory

Source activity

Readings a source repeats on a schedule, counted rather than listed.

5×ModifiedAug 18, 2026 · SOCRadar CTI
2×Tweets · 1 time tweeted.Jun 26, 2026 – Jun 27, 2026 · SOCRadar CTI
1×SVRS is calculatedJun 26, 2026 · SOCRadar CTI

References

4 on the record

github.com/Netflix/lemur/commit/872f6e282542352f2bf3f6e2bcc504ab81e1843d
Exploit, Third Party Advisory, NIST, Mitre
github.com/Netflix/lemur/releases/tag/v1.9.2
Exploit, Third Party Advisory, NIST, Mitre
github.com/Netflix/lemur/security/advisories/GHSA-v2wp-frmc-5q3v
Exploit, Third Party Advisory, NIST, Mitre
github.com/advisories/GHSA-v2wp-frmc-5q3v
Exploit, Third Party Advisory

Elsewhere on this site

Netflixevery CVE for this vendor
pipevery CVE for this vendor
SSRFsame class
CWE-285other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-55166 is Lemur: any SSO-authenticated user achieves AWS IAM compromise and permanent PKI key access via ACME acme_url SSRF and creator-equality IDOR, a critical vulnerability affecting lemur from Netflix, pip. The current evidence does not list it in CISA KEV, and the exploit status is: Active exploitation is not confirmed from current sources for CVE-2026-55166. Public exploit evidence is: A public PoC is not confirmed from current sources for CVE-2026-55166. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 9.9 describes technical severity, while EPSS 0% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.