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Fix SNMP infinite recursion & type detection #1930

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Merged
merged 2 commits into from
Mar 30, 2019
Merged

Fix SNMP infinite recursion & type detection #1930

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77a5e2a
Fix SNMP infinite recursion & type detection
gpotter2 Mar 24, 2019
6025d9e
Better string type test
p-l- Mar 25, 2019
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8 changes: 6 additions & 2 deletions scapy/asn1/ber.py
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Original file line number Diff line number Diff line change
Expand Up @@ -264,14 +264,18 @@ def do_dec(cls, s, context=None, safe=False):
if context is None:
context = cls.tag.context
cls.check_string(s)
p, _ = BER_id_dec(s)
p, remainder = BER_id_dec(s)
if p not in context:
t = s
if len(t) > 18:
t = t[:15] + b"..."
raise BER_Decoding_Error("Unknown prefix [%02x] for [%r]" %
(p, t), remaining=s)
codec = context[p].get_codec(ASN1_Codecs.BER)
if codec == BERcodec_Object:
# Value type defined as Unknown
l, s = BER_num_dec(remainder)
return ASN1_BADTAG(s[:l]), s[l:]
return codec.dec(s, context, safe)

@classmethod
Expand All @@ -294,7 +298,7 @@ def safedec(cls, s, context=None):

@classmethod
def enc(cls, s):
if isinstance(s, six.string_types):
if isinstance(s, six.string_types + (bytes,)):
return BERcodec_STRING.enc(s)
else:
return BERcodec_INTEGER.enc(int(s))
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14 changes: 14 additions & 0 deletions test/regression.uts
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Expand Up @@ -1155,6 +1155,20 @@ assert SNMP in z
x = UDP()/SNMP()
assert x.sport == x.dport == 161

= Basic SNMPvarbind build
~ SNMP ASN1
x = SNMPvarbind(oid=ASN1_OID("1.3.6.1.2.1.1.4.0"), value=RandBin())
x = SNMPvarbind(raw(x))
assert isinstance(x.value, ASN1_STRING)

= Failing SNMPvarbind dissection
~ SNMP ASN1
try:
SNMP('0a\x02\x01\x00\x04\x06public\xa3T\x02\x02D\xd0\x02\x01\x00\x02\x01\x000H0F\x06\x08+\x06\x01\x02\x01\x01\x05\x00\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D\x00\x03\x01\x02D')
assert False
except BER_Decoding_Error:
pass

= ASN1 - ASN1_Object
assert ASN1_Object(1) == ASN1_Object(1)
assert ASN1_Object(1) > ASN1_Object(0)
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