Dnslib3

A library to encode/decode DNS wire-format packets.

The library provides:

Support for encoding/decoding DNS packets between wire format, python objects, and Zone/DiG textual representation (dnslib.dns)
A server framework allowing the simple creation of custom DNS resolvers (dnslib.server) and a number of example servers created using this framework
A number of utilities for testing (dnslib.client, dnslib.proxy, dnslib.intercept)

Python 3 support was added in Version 0.9.0 which represented a fairly major update to the library - the key changes include:

The 'Bimap' interface was changed significantly to explicitly split forward (value->text) lookups via getitem and reverse (text->value) lookups via getattr. Applications using the old interface will need to be updated.
Hostnames are now returned with a trailing dot by default (in line with RFC)
Most object attributes are now typed in line with the record definitions to make it harder to generate invalid packets
Support for encoding/decoding resource records in 'Zone' (BIND) file format
Support for encoding/decoding packets in 'DiG' format
Server framework allowing (in most cases) custom resolvers to be created by just subclassing the DNSResolver class and overriding the 'resolve' method
A lot of fixes to error detection/handling which should make the library much more robust to invalid/unsupported data. The library should now either return a valid DNSRecord instance when parsing a packet or raise DNSError (tested via fuzzing)
Improved utilities (dnslib.client, dnslib.proxy, dnslib.intercept)
Improvements to encoding/decoding tests including the ability to generate test data automatically in test_decode.py (comparing outputs against DiG)
Ability to compare and diff DNSRecords

Classes

The key DNS packet handling classes are in dnslib.dns and map to the standard DNS packet sections:

DNSRecord - container for DNS packet. Contains:
- DNSHeader
- Question section containing zero or more DNSQuestion objects
- Answer section containing zero or more RR objects
- Authority section containing zero or more RR objects
- Additional section containing zero or more RR objects
DNS RRs (resource records) contain an RR header and an RD object)
Specific RD types are implemented as subclasses of RD
DNS labels are represented by a DNSLabel class - in most cases this handles conversion to/from textual representation however does support arbitatry labels via a tuple of bytes objects

Usage

To decode a DNS packet:

>>> packet = binascii.unhexlify(b'd5ad818000010005000000000377777706676f6f676c6503636f6d0000010001c00c0005000100000005000803777777016cc010c02c0001000100000005000442f95b68c02c0001000100000005000442f95b63c02c0001000100000005000442f95b67c02c0001000100000005000442f95b93')
>>> d = DNSRecord.parse(packet)
>>> d
<DNS Header: id=0xd5ad type=RESPONSE opcode=QUERY flags=RD,RA rcode='NOERROR' q=1 a=5 ns=0 ar=0>
<DNS Question: 'www.google.com.' qtype=A qclass=IN>
<DNS RR: 'www.google.com.' rtype=CNAME rclass=IN ttl=5 rdata='www.l.google.com.'>
<DNS RR: 'www.l.google.com.' rtype=A rclass=IN ttl=5 rdata='66.249.91.104'>
<DNS RR: 'www.l.google.com.' rtype=A rclass=IN ttl=5 rdata='66.249.91.99'>
<DNS RR: 'www.l.google.com.' rtype=A rclass=IN ttl=5 rdata='66.249.91.103'>
<DNS RR: 'www.l.google.com.' rtype=A rclass=IN ttl=5 rdata='66.249.91.147'>

The default text representation of the DNSRecord is in zone file format:

>>> print(d)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54701
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.google.com.                IN      A
;; ANSWER SECTION:
www.google.com.         5       IN      CNAME   www.l.google.com.
www.l.google.com.       5       IN      A       66.249.91.104
www.l.google.com.       5       IN      A       66.249.91.99
www.l.google.com.       5       IN      A       66.249.91.103
www.l.google.com.       5       IN      A       66.249.91.147

To create a DNS Request Packet:

>>> d = DNSRecord.question("google.com")

(This is equivalent to: d = DNSRecord(q=DNSQuestion("google.com") )

>>> d
<DNS Header: id=... type=QUERY opcode=QUERY flags=RD rcode='NOERROR' q=1 a=0 ns=0 ar=0>
<DNS Question: 'google.com.' qtype=A qclass=IN>

>>> str(DNSRecord.parse(d.pack())) == str(d)
True

>>> print(d)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;google.com.                    IN      A

>>> d = DNSRecord.question("google.com","MX")

(This is equivalent to: d = DNSRecord(q=DNSQuestion("google.com",QTYPE.MX) )

>>> str(DNSRecord.parse(d.pack())) == str(d)
True

>>> print(d)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;google.com.                    IN      MX

To create a DNS Response Packet:

>>> d = DNSRecord(DNSHeader(qr=1,aa=1,ra=1),
...               q=DNSQuestion("abc.com"),
...               a=RR("abc.com",rdata=A("1.2.3.4")))
>>> d
<DNS Header: id=... type=RESPONSE opcode=QUERY flags=AA,RD,RA rcode='NOERROR' q=1 a=1 ns=0 ar=0>
<DNS Question: 'abc.com.' qtype=A qclass=IN>
<DNS RR: 'abc.com.' rtype=A rclass=IN ttl=0 rdata='1.2.3.4'>
>>> str(DNSRecord.parse(d.pack())) == str(d)
True

>>> print(d)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com.                       IN      A
;; ANSWER SECTION:
abc.com.                0       IN      A       1.2.3.4

It is also possible to create RRs from a string in zone file format

>>> RR.fromZone("abc.com IN A 1.2.3.4")
[<DNS RR: 'abc.com.' rtype=A rclass=IN ttl=0 rdata='1.2.3.4'>]

(Note: this produces a list of RRs which should be unpacked if being
passed to add_answer/add_auth/add_ar etc)

>>> q = DNSRecord.question("abc.com")
>>> a = q.reply()
>>> a.add_answer(*RR.fromZone("abc.com 60 A 1.2.3.4"))
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com.                       IN      A
;; ANSWER SECTION:
abc.com.                60      IN      A       1.2.3.4

The zone file can contain multiple entries and supports most of the normal format defined in RFC1035 (specifically not $INCLUDE)

>>> z = '''
...         $TTL 300
...         $ORIGIN abc.com
...
...         @       IN      MX      10  mail.abc.com.
...         www     IN      A       1.2.3.4
...                 IN      TXT     "Some Text"
...         mail    IN      CNAME   www.abc.com.
... '''
>>> for rr in RR.fromZone(textwrap.dedent(z)):
...     print(rr)
abc.com.                300     IN      MX      10 mail.abc.com.
www.abc.com.            300     IN      A       1.2.3.4
www.abc.com.            300     IN      TXT     "Some Text"
mail.abc.com.           300     IN      CNAME   www.abc.com.

To create a skeleton reply to a DNS query:

>>> q = DNSRecord(q=DNSQuestion("abc.com",QTYPE.ANY))
>>> a = q.reply()
>>> a.add_answer(RR("abc.com",QTYPE.A,rdata=A("1.2.3.4"),ttl=60))
>>> str(DNSRecord.parse(a.pack())) == str(a)
True
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com.                       IN      ANY
;; ANSWER SECTION:
abc.com.                60      IN      A       1.2.3.4

Add additional RRs:

>>> a.add_answer(RR("xxx.abc.com",QTYPE.A,rdata=A("1.2.3.4")))
>>> a.add_answer(RR("xxx.abc.com",QTYPE.AAAA,rdata=AAAA("1234:5678::1")))
>>> str(DNSRecord.parse(a.pack())) == str(a)
True
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com.                       IN      ANY
;; ANSWER SECTION:
abc.com.                60      IN      A       1.2.3.4
xxx.abc.com.            0       IN      A       1.2.3.4
xxx.abc.com.            0       IN      AAAA    1234:5678::1

It is also possible to create a reply from a string in zone file format:

>>> q = DNSRecord(q=DNSQuestion("abc.com",QTYPE.ANY))
>>> a = q.replyZone("abc.com 60 IN CNAME xxx.abc.com")
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com.                       IN      ANY
;; ANSWER SECTION:
abc.com.                60      IN      CNAME   xxx.abc.com.

>>> str(DNSRecord.parse(a.pack())) == str(a)
True

>>> q = DNSRecord(q=DNSQuestion("abc.com",QTYPE.ANY))
>>> a = q.replyZone(textwrap.dedent(z))
>>> print(a)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;abc.com.                       IN      ANY
;; ANSWER SECTION:
abc.com.                300     IN      MX      10 mail.abc.com.
www.abc.com.            300     IN      A       1.2.3.4
www.abc.com.            300     IN      TXT     "Some Text"
mail.abc.com.           300     IN      CNAME   www.abc.com.

To send a DNSSEC request (EDNS OPT record with DO flag & header AD flag):

>>> q = DNSRecord(q=DNSQuestion("abc.com",QTYPE.A))
>>> q.add_ar(EDNS0(flags="do",udp_len=4096))
>>> q.header.ad = 1
>>> print(q)
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: ...
;; flags: rd ad; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; QUESTION SECTION:
;abc.com.                       IN      A
;; ADDITIONAL SECTION:
;; OPT PSEUDOSECTION
; EDNS: version: 0, flags: do; udp: 4096

Note that when using the library you should always validate the received TXID

q = DNSRecord.question("abc.com")
a_pkt = q.send(address,port,tcp=args.tcp)
a = DNSRecord.parse(a_pkt)
if q.header.id != a.header.id:
    raise DNSError('Response transaction id does not match query transaction id')

The library also includes a simple framework for generating custom DNS resolvers in dnslib.server (see module docs). In most cases this just requires implementing a custom 'resolve' method which receives a question object and returns a response.

A number of sample resolvers are provided as examples (see CLI --help):

dnslib.fixedresolver - Respond to all requests with fixed response
dnslib.zoneresolver - Respond from Zone file
dnslib.shellresolver - Call shell script to generate response

The library includes a number of client utilities:

DiG like client library
```
# python -m dnslib.client --help
```
DNS Proxy Server
```
# python -m dnslib.proxy --help
```
Intercepting DNS Proxy Server (replace proxy responses for specified domains)
```
# python -m dnslib.intercept --help
```

Changelog

 *   0.1     2010-09-19  Initial Release
 *   0.2     2010-09-22  Minor fixes
 *   0.3     2010-10-02  Add DNSLabel class to support arbitrary labels (embedded '.')
 *   0.4     2012-02-26  Merge with dbslib-circuits
 *   0.5     2012-09-13  Add support for RFC2136 DDNS updates
                         Patch provided by Wesley Shields <wxs@FreeBSD.org> - thanks
 *   0.6     2012-10-20  Basic AAAA support
 *   0.7     2012-10-20  Add initial EDNS0 support (untested)
 *   0.8     2012-11-04  Add support for NAPTR, Authority RR and additional RR
                         Patch provided by Stefan Andersson (https://bitbucket.org/norox) - thanks
 *   0.8.1   2012-11-05  Added NAPTR test case and fixed logic error
                         Patch provided by Stefan Andersson (https://bitbucket.org/norox) - thanks
 *   0.8.2   2012-11-11  Patch to fix IPv6 formatting
                         Patch provided by Torbjorn Lonnemark (https://bitbucket.org/tobbezz) - thanks
 *   0.8.3   2013-04-27  Don't parse rdata if rdlength is 0
                         Patch provided by Wesley Shields <wxs@FreeBSD.org> - thanks
 *   0.9.0   2014-05-05  Major update including Py3 support (see docs)
 *   0.9.1   2014-05-05  Minor fixes
 *   0.9.2   2014-08-26  Fix Bimap handling of unknown mappings to avoid exception in printing
                         Add typed attributes to classes
                         Misc fixes from James Mills - thanks
 *   0.9.3   2014-08-26  Workaround for argparse bug which raises AssertionError if [] is
                         present in option text (really?)
 *   0.9.4   2015-04-10  Fix to support multiple strings in TXT record
                         Patch provided by James Cherry (https://bitbucket.org/james_cherry) - thanks
                         NOTE: For consistency this patch changes the 'repr' output for
                               TXT records to always be quoted
 *   0.9.5   2015-10-27  Add threading & timeout handling to DNSServer
 *   0.9.6   2015-10-28  Replace strftime in RRSIG formatting to avoid possible locale issues
                         Identified by Bryan Everly - thanks
 *   0.9.7   2017-01-15  Sort out CAA/TYPE257 DiG parsing mismatch
 *   0.9.8   2019-02-25  Force DNSKEY key to be bytes object
                         Catch Bimap __wrapped__ attr (used by inspect module in 3.7)
 *   0.9.9   2019-03-19  Add support for DNSSEC flag getters/setters (from <raul@dinosec.com> - thanks)
                         Added --dnssec flags to dnslib.client & dnslib.test_decode (sets EDNS0 DO flag)
                         Added EDNS0 support to dnslib.digparser
 *   0.9.10  2019-03-24  Fixes to DNSSEC support
                         Add NSEC RR support
                         Add --dnssec flag to dnslib.client & dnslib.test_decode
                         Quote/unquote non-printable characters in DNS labels
                         Update test data
                         (Thanks to <raul@dinosec.com> for help)
 *   0.9.11  2019-12-17  Encode NOTIFY Opcode (Issue #26)
 *   0.9.12  2019-12-17  Transition master repository to Github (Bitbucket shutting down hg)
 *   0.9.13  2020-06-01  Handle truncated requests in server.py (Issue #9)
                         Replace thred.isAlive with thread.is_alive (Deprecated in Py3.9)
                         Merged Pull Request #4 (Extra options for intercept.py) - thanks to @nolanl
 *   0.9.14  2020-06-09  Merged Pull Request #10 (Return doctest status via exit code)
                         Thanks to @mgorny
 *   0.9.15  2021-05-07  DNSServer fixes - support IPv6 (from Pull Request #21) - thanks to @mikma
                                         - deamon threads (Pull Request #19) - thanks to @wojons
                         Add unsupported RR types (Issue #27)
 *   0.9.16  2021-05-07  Merge pull request #23 from Tugzrida/patch-1
                            Add support for all RR types to NSEC type bitmap
                         Merge pull request #17 from sunds/issue_16
                            Issue 16: uncaught exceptions leak open sockets
 *   0.9.18  2022-01-09  Validate TXID in client.py (Issue #30 - thanks to @daniel4x)
 *   0.9.19  2022-01-09  Allow custom log function (logf) in  DNSLogger
                            (Issue #31 - thanks to @DmitryFrolovTri)
 *   0.9.20  2022-07-17  Fix DeprecationWarnings about invalid escape sequences
                            (Pull-Request #39 - thanks to @brianmaissy)
                         Make DNSLabel matchSuffix and stripSuffix case-insensitive
                            (Pull-Request #37 - thanks to @NiKiZe)
                         Add support for HTTPS RR
                            (Pull-Request #35 - thanks to @jkl-caliber)
                         Fix display of non-printable characters in TXT records
                            (Issue #32 - thanks to @sbv-csis)
                         Add --strip-aaaa option to dnslib.proxy
 *   0.9.21  2022-09-19  Minor clean-up / add wheels to distro
 *   0.9.22  2022-09027  Issue #43 (0.9.21 Raises TypeError instead of DNSError when failing to parse HTTPS records)
                         Note that we just fix the exception - there still seems to be a problem with parsing HTTPS records
                         (Thanks to @robinlandstrom)
 *   0.9.23  2022-10-28  Issue #43: HTTPS reads after RD end (thanks to @robinlandstrom for pull request)
                         Issue #45: Dnslib fails to handle unknown RR types in NSEC RD type bitmap
                            Bimap now supports a function to map unknown types which we use to
                            dynamically map from rtype <-> TYPExxxx for unknown record types
                            RR zone representation updated to match RFC3597
                         Pull Request #47: Add support for DS, SSHFP, and TLSA records (thanks to @rmbolger)
 *   0.9.24  2024-01-02  Merge multiple PRs
                            #49 - Generate README.md (via symlink)
                            #51 - Update Github CI checkout & setup-python actions (and remove Python 2.7 CI support)
                                  (thanks to @SpencerIsGiddy)
                            #54 - Support for RP records (thanks to @ryan-gang)
                            #57 - Support for LOC records (thanks to @valentinesd)
                         (Note that this will be the last release supporting Python 2.7 and Python <3.7)

License

BSD

Alviner / dnslib3

readme

Dnslib3

Classes

Usage

Changelog

License