solderpunk
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AV-98
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Present expiration information about previous certificates in TOFU warning messages.

This commit is contained in:
Solderpunk 2020-05-23 12:53:02 +02:00
parent e455d2ec85
commit 7a3f1c77a5
1 changed files with 18 additions and 2 deletions
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av98.py
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@ -706,9 +706,11 @@ Slow internet connection? Use 'set timeout' to be more patient.""")
# If so, check for a match
if cached_certs:
max_count = 0
most_frequent_cert = None
for cached_fingerprint, first, last, count in cached_certs:
if count > max_count:
max_count = count
most_frequent_cert = cached_fingerprint
if fingerprint == cached_fingerprint:
# Matched!
self._debug("TOFU: Accepting previously seen ({} times) certificate {}".format(count, fingerprint))
@ -719,12 +721,27 @@ Slow internet connection? Use 'set timeout' to be more patient.""")
self.db_conn.commit()
break
else:
if _HAS_CRYPTOGRAPHY:
# Load the most frequently seen certificate to see if it has
# expired
certdir = os.path.join(self.config_dir, "cert_cache")
with open(os.path.join(certdir, most_frequent_cert+".crt"), "rb") as fp:
previous_cert = fp.read()
previous_cert = x509.load_der_x509_certificate(previous_cert, _BACKEND)
previous_ttl = previous_cert.not_valid_after - now
print(previous_ttl)
self._debug("TOFU: Unrecognised certificate {}! Raising the alarm...".format(fingerprint))
print("****************************************")
print("[SECURITY WARNING] Unrecognised certificate!")
print("The certificate presented for {} ({}) has never been seen before.".format(host, address))
print("A different certificate has previously been seen {} times.".format(max_count))
print("This MIGHT be a Man-in-the-Middle attack.")
print("A different certificate has previously been seen {} times.".format(max_count))
if _HAS_CRYPTOGRAPHY:
if previous_ttl < datetime.timedelta():
print("That certificate has expired, which reduces suspicion somewhat.")
else:
print("That certificate is still valid for: {}".format(previous_ttl))
print("****************************************")
print("Attempt to verify the new certificate fingerprint out-of-band:")
print(fingerprint)
@ -734,7 +751,6 @@ Slow internet connection? Use 'set timeout' to be more patient.""")
VALUES (?, ?, ?, ?, ?, ?)""",
(host, address, fingerprint, now, now, 1))
self.db_conn.commit()
certdir = os.path.join(self.config_dir, "cert_cache")
with open(os.path.join(certdir, fingerprint+".crt"), "wb") as fp:
fp.write(cert)
else: