47 lines
1.5 KiB
Markdown
47 lines
1.5 KiB
Markdown
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Problem
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Incorrect parsing of large list element sizes may lead to CPU usage amplification attack
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Discovered by
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=============
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Martin Dindoffer <contact@dindoffer.eu>
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Announced
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=========
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2021-10-04
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Impact
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======
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It is possible for an attacker to craft a small malicious message that will contain large lists with no data, leading to
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artificial load on the system and possibly a Denial of Service attack.
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CVSS score
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==========
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5.9 (Medium) CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
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Fixed in
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========
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Release 0.1.12
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Details
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=======
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A tag pointer encodes the size of the elements in words and the total number of elements. Validation of these values is
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performed in the code, but only as an overflow check of their product (against the total wordcount encoded in the list
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pointer). The element size is read as a `short` value with improper casting to signed integers. Therefore, it is
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possible to craft a message that will encode a large amount of elements (up to `2^30`) and offset this bloated size by
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specifying a negative size of the elements (in words). There is no need to encode the actual payload for the large list,
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thus capnproto-java will generate Iterators with large iteration counts over empty payload with messages of well under
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100 bytes, that may put CPU under loads heavy enough to easily perform DoS attacks.
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Remediation
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===========
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The `short` values of the list element sizes are now parsed as unsigned values, making sure that the list overflow check
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will catch the huge list size.
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