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Bug #3628
closedIncorrect ASN.1 long form length parsing
Affected Versions:
Effort:
low
Difficulty:
low
Label:
Needs backport to 4.1, Needs backport to 5.0
Description
Currently the definite long form is parsed as an additive length. This
https://github.com/OISF/suricata/blob/suricata-5.0.2/src/util-decode-asn1.c#L157
8.1.3.5 In the long form, the length octets shall consist of an initial octet and one or more subsequent octets.
https://www.itu.int/rec/T-REC-X.690-201508-I/en
A more digestible explanation is given here with an example
For the definite form, if the length is less than 128, you just use a single byte, with the high bit set to zero. Otherwise the high bit is set to one, and the low seven bits set to the length of length. The length is then encoded in that many bytes.
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