PowerDNS Security Advisory 2026-09 for DNSdist: Multiple issues

[Remi Gacogne <remi.gacogne () powerdns com>]

Hi all,

Today we released two new versions of DNSdist, 1.9.12 and 2.0.3, fixing 
several security issues that have been reported to us. These security 
issues are low-severity or involve unusual configurations.

The issues fixed in these releases are:

- CVE-2026-40011: An attacker sending a large number of crafted DNS 
queries might be able to trigger a dynamic block being inserted with a 
value causing invalid output to be produced in the prometheus endpoint. 
The prometheus endpoint will then be rejected by the scraper until the 
dynamic block expires.
- CVE-2026-42004: An attacker can send a crafted EDNS OPT record that 
will be ignored by DNSdist's filtering rules, but will be rewritten as a 
valid OPT record when EDNS Client Subnet is inserted, causing the 
backend to see the EDNS option(s) that DNSdist did not filter.
- CVE-2026-42005: An attacker can send a web request that causes 
unlimited memory allocation in the internal web server, leading to a 
denial of service. The internal web server is disabled by default.
- CVE-2026-40208: An attacker might be able to delay the processing of 
DoH3 queries by sending DoH3 GET queries with an invalid DATA frame.
- CVE-2026-40209: An attacker might be able to cause outgoing TCP 
connections to backend to be stuck until a timeout occurs instead of 
being released immediately. This could be used to cause a denial of 
service if there is a limit to the number of concurrent connections to 
this backend, or if the process runs out of file descriptors.
- CVE-2026-40210: An out-of-bounds read might happen when 
SetMacAddrAction is used, potentially resulting in uninitialized memory 
being sent over the network or a crash.
- CVE-2026-40211: An attacker can send crafted DNS over HTTP/3 queries, 
triggering an exception that prevents some buffer from being freed right 
away. The buffer will be freed at the end of the QUIC connection, but on 
some setups it might be possible to open enough concurrent DoH3 streams 
to trigger an out-of-memory condition, resulting in a denial of service.


The full security advisory can be found at 
https://www.dnsdist.org/security-advisories/powerdns-advisory-for-dnsdist-2026-09.html 
and below.

Please feel free to contact me directly if you have any question.


PowerDNS Security Advisory 2026-09 for DNSdist: Multiple issues
===============================================================

CVE-2026-40011: Prometheus denial of service via crafted DNS queries
--------------------------------------------------------------------

- CVE: CVE-2026-40011
- Date: 2026-06-25T00:00:00+01:00
- Discovery date: 2026-04-07T00:00:00+01:00
- Affects: PowerDNS DNSdist up to and including 2.0.6 and 1.9.14
- Not affected: PowerDNS DNSdist 1.9.15, 2.0.7
- Severity: Medium
- Impact: Denial of service
- Exploit: This problem can be triggered by a client sending crafted queries
- Risk of system compromise: None
- Solution: Upgrade to patched version or don't use 
dynBlockRulesGroup():setSuffixMatchRule() or 
dynBlockRulesGroup():setSuffixMatchRuleFFI()
- CWE: CWE-116
- CVSS: 3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- Last affected: 1.9.14,2.0.6
- First fixed: 1.9.15,2.0.7
- Internal ID: 462

An attacker sending a large number of crafted DNS queries might be able 
to trigger a dynamic block being inserted with a value causing invalid 
output to be produced in the prometheus endpoint. The prometheus 
endpoint will then be rejected by the scraper until the dynamic block 
expires.

`CVSS Score: 3.7 
<https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N&version=3.1>`__

The remedy is: upgrade to a patched version or don't use 
dynBlockRulesGroup():setSuffixMatchRule() or 
dynBlockRulesGroup():setSuffixMatchRuleFFI().

We would like to thank Haruki Oyama (Waseda University) for bringing 
this issue to our attention.

CVE-2026-42004: EDNS options smuggling
--------------------------------------

- CVE: CVE-2026-42004
- Date: 2026-06-25T00:00:00+01:00
- Discovery date: 2026-04-24T00:00:00+01:00
- Affects: PowerDNS DNSdist up to and including 2.0.6 and 1.9.14
- Not affected: PowerDNS DNSdist 1.9.15, 2.0.7
- Severity: Low
- Impact: Bypass of security rules
- Exploit: This problem can be triggered by a client sending crafted DNS 
queries
- Risk of system compromise: None
- Solution: Upgrade to patched version, do not rely on EDNS option 
filtering or do not enable EDNS Client Subnet insertion
- CWE: CWE-115
- CVSS: 3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- Last affected: 1.9.14,2.0.6
- First fixed: 1.9.15,2.0.7
- Internal ID: 490

An attacker can send a crafted EDNS OPT record that will be ignored by 
DNSdist's filtering rules, but will be rewritten as a valid OPT record 
when EDNS Client Subnet is inserted, causing the backend to see the EDNS 
option(s) that DNSdist did not filter.

CVSS Score: 3.7 
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N&version=3.1

The remedy is: upgrade to a patched version, do not rely on EDNS option 
filtering or do not enable EDNS Client Subnet insertion.

We would like to thank Vitaly Simonovich for bringing this issue to our 
attention.

CVE-2026-42005: Insufficient input validation of internal web server
--------------------------------------------------------------------

- CVE: CVE-2026-42005
- Date: 2026-06-25T00:00:00+01:00
- Discovery date: 2026-04-25T00:00:00+01:00
- Affects: PowerDNS DNSdist up to and including 2.0.6 and 1.9.14
- Not affected: PowerDNS DNSdist 1.9.15, 2.0.7
- Severity: Medium
- Impact: Denial of service
- Exploit: This problem can be triggered by a client sending crafted 
HTTP queries
- Risk of system compromise: None
- Solution: Upgrade to patched version or do not enable the internal 
webserver
- CWE: CWE-770
- CVSS: 3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
- Last affected: 1.9.14,2.0.6
- First fixed: 1.9.15,2.0.7
- Internal ID: 481

An attacker can send a web request that causes unlimited memory 
allocation in the internal web server, leading to a denial of service. 
The internal web server is disabled by default.

CVSS Score: 4.3 
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L&version=3.1

The remedy is: upgrade to a patched version, or prevent network access 
to the internal webserver. In general for defense in-depth reasons we 
recommend making the internal web server only accessible to trusted clients.

We would like to thank ilya rozentsvaig for bringing this issue to our 
attention.

CVE-2026-40208: Denial of service via DoH3 queries
--------------------------------------------------

- CVE: CVE-2026-40208
- Date: 2026-06-25T00:00:00+01:00
- Discovery date: 2026-04-13T00:00:00+01:00
- Affects: PowerDNS DNSdist up to and including 2.0.6 and 1.9.14
- Not affected: PowerDNS DNSdist 1.9.15, 2.0.7
- Severity: Low
- Impact: Denial of service
- Exploit: This problem can be triggered by a client sending crafted 
DoH3 queries
- Risk of system compromise: None
- Solution: Upgrade to patched version or do not enable DoH3
- CWE: CWE-705
- CVSS: 3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
- Last affected: 1.9.14,2.0.6
- First fixed: 1.9.15,2.0.7
- Internal ID: 472

An attacker might be able to delay the processing of DoH3 queries by 
sending DoH3 GET queries with an invalid DATA frame.

CVSS Score: 3.7 
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L&version=3.1

The remedy is: upgrade to a patched version or disable DNS over HTTP/3

We would like to thank ylwango613 for bringing this issue to our attention.

CVE-2026-40209: Denial of service via IXFR queries
--------------------------------------------------

- CVE: CVE-2026-40209
- Date: 2026-06-25T00:00:00+01:00
- Discovery date: 2026-04-13T00:00:00+01:00
- Affects: PowerDNS DNSdist up to and including 2.0.6 and 1.9.14
- Not affected: PowerDNS DNSdist 1.9.15, 2.0.7
- Severity: Medium
- Impact: Denial of service
- Exploit: This problem can be triggered by a client sending crafted 
IXFR queries
- Risk of system compromise: None
- Solution: Upgrade to patched version or block incoming IXFR queries
- CWE: CWE-772
- CVSS: 3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Last affected: 1.9.14,2.0.6
- First fixed: 1.9.15,2.0.7
- Internal ID: 471

An attacker might be able to cause outgoing TCP connections to backend 
to be stuck until a timeout occurs instead of being released 
immediately. This could be used to cause a denial of service if there is 
a limit to the number of concurrent connections to this backend, or if 
the process runs out of file descriptors.

CVSS Score: 5.3 
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L&version=3.1

The remedy is: upgrade to a patched version or block incoming IXFR 
queries with: addAction(QTypeRule(DNSQType.IXFR), 
RCodeAction(DNSRCode.REFUSED))

We would like to thank Qifan Zhang (Palo Alto Networks) for bringing 
this issue to our attention.

CVE-2026-40210: Out-of-bounds read in SetMacAddrAction
------------------------------------------------------

- CVE: CVE-2026-40210
- Date: 2026-06-25T00:00:00+01:00
- Discovery date: 2026-04-13T00:00:00+01:00
- Affects: PowerDNS DNSdist up to and including 2.0.6 and 1.9.14
- Not affected: PowerDNS DNSdist 1.9.15, 2.0.7
- Severity: Low
- Impact: Denial of service or Information disclosure
- Exploit: This problem can be triggered by a client sending DNS queries 
when SetMacAddrAction is used
- Risk of system compromise: None
- Solution: Upgrade to patched version or do not use SetMacAddrAction
- CWE: CWE-126
- CVSS: 3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L
- Last affected: 1.9.14,2.0.6
- First fixed: 1.9.15,2.0.7
- Internal ID: 469

An out-of-bounds read might happen when SetMacAddrAction is used, 
potentially resulting in uninitialized memory being sent over the 
network or a crash.

CVSS Score: 4.8 
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L&version=3.1

The remedy is: upgrade to a patched version or do not use SetMacAddrAction

We would like to thank Qifan Zhang (Palo Alto Networks) for bringing 
this issue to our attention.

CVE-2026-40211: Denial of service via crafted DoH3 queries
----------------------------------------------------------

- CVE: CVE-2026-40211
- Date: 2026-06-25T00:00:00+01:00
- Discovery date: 2026-04-09T00:00:00+01:00
- Affects: PowerDNS DNSdist up to and including 2.0.6 and 1.9.14
- Not affected: PowerDNS DNSdist 1.9.15, 2.0.7
- Severity: Medium
- Impact: Denial of service
- Exploit: This problem can be triggered by a client sending crafted 
DoH3 queries
- Risk of system compromise: None
- Solution: Upgrade to patched version or do not enable DoH3
- CWE: CWE-770
- CVSS: 3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Last affected: 1.9.14,2.0.6
- First fixed: 1.9.15,2.0.7
- Internal ID: 465

An attacker can send crafted DNS over HTTP/3 queries, triggering an 
exception that prevents some buffer from being freed right away. The 
buffer will be freed at the end of the QUIC connection, but on some 
setups it might be possible to open enough concurrent DoH3 streams to 
trigger an out-of-memory condition, resulting in a denial of service.

CVSS Score: 5.3 
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L&version=3.1

The remedy is: upgrade to a patched version or do not enable DNS over HTTP/3

We would like to thank Mehtab Zafar for bringing this issue to our 
attention.


Best regards,
--
Remi Gacogne
PowerDNS.COM BV - https://www.powerdns.com/

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