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Date: Thu, 9 Aug 2018 08:06:36 +0200
From: Petr Špaček <>
Subject: Knot Resolver 2.4.1 security release


this is copy of e-mail for distros@ mailing list.

Fixed version 2.4.1 is already available from

I apologize for delay between release and this post.
Petr Špaček  @  CZ.NIC

-------- Forwarded Message --------
Subject: [vs] Knot Resolver 2.4.1 security release + CVE request
Date: Wed, 1 Aug 2018 16:47:14 +0200
From: Petr Špaček <>
Organization: CZ.NIC


this is pre-release advisory about bugs affecting security of Knot
Resolver (a DNS resolver by CZ.NIC).

Under certain circumstances this bug allows an attacker to hijack
DNS domains.

Unembargo date
Thursday 2nd August 2018 12:00 (noon) GMT

Minimal patch on top of version 2.4.0 is in attached fix.patch.
The second file hardening.patch which provides additional hardening
(defense in depth but not strictly necessary). We will be releasing
version 2.4.1 with other fixes as well.

If you are interested we could provide encrypted tarball with 2.4.1
sooner so you can build version with other fixes as well, just let me know.

CVE assignment request
[Requestors emails address (required)]:

[I confirm that this CVE is for an Open Source software
component/library/etc. (required)]:

[I confirm that I have read the CVE Terms of Use and agree to them

[Vendor/Project of the product (required)]:

[Affected product name (required)]:
Knot Resolver

[Product URL (required)]:

[Affected version (required)]:
Knot Resolver <= 2.4.0

[Fixed version (optional)]:
Knot Resolver 2.4.1

[Vulnerability type (required)]:
CWE-20: Improper Input Validation

[Affected component (required)]:

[Impact of exploitation (required)]:
Under certain circumstances this bug allows an attacker to hijack
DNS domains.

[Description of vulnerability]:
Improper input validation bug in DNS resolver component of Knot
Resolver allows remote attacker to poison cache.

To execute this attack the attacker has to have:
+ access to rogue authoritative server and
+ ability to trigger query from resolver under attack to authoritative
server under attacker's control

For successful exploitation the data used to poison cache need to match
certain criteria which we decided not to disclose at the moment.

Please note that "classical" DNS answer spoofing is going to be very
hard because Knot Resolver randomizes ports, query ID, and query name
capitalization - i.e. plain Kaminsky attack will be difficult. This is
why attacker needs to control an authoritative server.

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): None
Scope (S): Unchanged
Confidentiality (C): None
Integrity (I): High
Availability (A): None

Technical Details:

CZ.NIC would like to thank Marek Vavrusa for reporting this issue.

[Reference URL 1 (required)]:

Thank you for processing this.

Petr Špaček  @  CZ.NIC

View attachment "fix.patch" of type "text/x-patch" (1348 bytes)

View attachment "hardening.patch" of type "text/x-patch" (2741 bytes)

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