Bug #5444: dns: allow dns messages with invalid opcodes - Suricata - Open Information Security Foundation

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Bug #5444

closed

dns: allow dns messages with invalid opcodes

Added by Jason Ish almost 2 years ago. Updated about 1 year ago.

Status:

Closed

Priority:

Normal

Assignee:

Jason Ish

Target version:

7.0.0-rc1

Affected Versions:

6.0.6

Effort:

Difficulty:

Label:

Description

Current a DNS message won't be detected as DNS if the opcode is considered invalid (greater than 7). We should probably accept any opcode, and then use rules to alert on invalid opcodes.

Research: Will this detect too much non DNS as DNS?

Files

opcode8.pcap (522 Bytes) opcode8.pcap

Jason Taylor, 07/19/2022 07:44 PM

Related issues 1 (0 open — 1 closed)

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Updated by Jason Taylor almost 2 years ago

File opcode8.pcap opcode8.pcap added

just adding a sample udp dns query with opcode of 8 set. With the change discussed in this ticket, a signature such as 'alert dns any any -> any any (msg:"dns opcode 8"; dns.opcode:8; sid:123; rev:1;)' run against the attached pcap would alert.

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Updated by Philippe Antoine over 1 year ago

To be noted : now that https://github.com/OISF/suricata/pull/7320 got merged, if a client sends junk to a DNS server, suricata will recognize the protocol as DNS (with app_proto_tc: failed)

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Updated by Victor Julien over 1 year ago

Priority changed from Normal to High
Label Needs backport to 6.0 added

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Updated by Victor Julien over 1 year ago

@Philippe Antoine are you saying that in master this issue is resolved (by the PR you mentioned)?

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Updated by Philippe Antoine over 1 year ago

That depends on how you define the issue.

If a DNS server uses invalid opcodes, as in the attached pcap, this issue is not resolved.

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Updated by Victor Julien over 1 year ago

Subtask #5550 added

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Updated by Victor Julien over 1 year ago

Label deleted (~~Needs backport to 6.0~~)

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Updated by Victor Julien over 1 year ago

Target version changed from 7.0.0-beta1 to 7.0.0-rc1

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Updated by Jason Ish over 1 year ago

Status changed from New to In Progress

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#10

Updated by Jason Ish over 1 year ago

Status changed from In Progress to In Review

PR: https://github.com/OISF/suricata/pull/8228

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#11

Updated by Philippe Antoine about 1 year ago

This ticket looks strange to me... What is the use case ?

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#12

Updated by Jason Ish about 1 year ago

Detect DNS with invalid opcodes. Currently if a DNS message has a bad opcode we don't detect it as DNS, even if it is.. Perhaps some DNS trickery.. We go blind to it. Bettern to parse it as DNS and provide the ability to detect invalid opcodes.

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#13