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Do not take a chain's root CA for a self-signed signer #597

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Merged
doomedraven merged 1 commit into from
Sep 25, 2026
Merged

Do not take a chain's root CA for a self-signed signer #597

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17 changes: 12 additions & 5 deletions modules/signatures/all/pe_cert_suspicious.py
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Original file line number Diff line number Diff line change
Expand Up @@ -62,12 +62,19 @@ def run(self):
ds = pe.get("digital_signers") or []
gs = pe.get("guest_signers") or {}

# A root CA signs itself, so a complete chain always holds a self-signed
# certificate. Only one that issued none of the others is the signer.
issuers = {
cert.get("issuer_commonName", "").lower()
for cert in ds
if cert.get("subject_commonName", "").lower() != cert.get("issuer_commonName", "").lower()
}
for cert in ds:
subject = cert.get("subject_commonName", "")
issuer = cert.get("issuer_commonName", "")
if not subject or not issuer:
continue
if subject.lower() != issuer.lower():
if subject.lower() != issuer.lower() or subject.lower() in issuers:
continue
if _is_known_ca(subject):
continue
Expand All @@ -80,12 +87,12 @@ def run(self):
)

if not self.data:
for signer in gs.get("aux_signers") or []:
if "Certificate Chain" not in (signer.get("name") or ""):
continue
chain = [s for s in gs.get("aux_signers") or [] if "Certificate Chain" in (s.get("name") or "")]
chain_issuers = {s.get("Issued by", "") for s in chain if s.get("Issued to") != s.get("Issued by")}
for signer in chain:
issued_to = signer.get("Issued to", "")
issued_by = signer.get("Issued by", "")
if issued_to and issued_to == issued_by and not _is_known_ca(issued_to):
if issued_to and issued_to == issued_by and issued_to not in chain_issuers and not _is_known_ca(issued_to):
self.data.append(
{
"subject": issued_to,
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