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                            CERT-Renater

                Note d'Information No. 2025/VULN453
_____________________________________________________________________

DATE                : 17/07/2025

HARDWARE PLATFORM(S): /

OPERATING SYSTEM(S): Systems running Bind versions prior to 9.20.11, 
                                         9.21.10.

=====================================================================
https://kb.isc.org/docs/cve-2025-40777
https://kb.isc.org/docs/cve-2025-40776
_____________________________________________________________________

CVE-2025-40777: A possible assertion failure when using the
'stale-answer-client-timeout 0' option


    Updated on Jul 16, 2025
    Published on Jul 16, 2025 

CVE: CVE-2025-40777

Document version: 2.0

Posting date: 16 July 2025

Program impacted: BIND

Versions affected:

BIND

    9.20.0 -> 9.20.10
    9.21.0 -> 9.21.9

(Versions prior to 9.18.0 were not assessed.)

BIND Supported Preview Edition

    9.20.9-S1 -> 9.20.10-S1

(Versions prior to 9.18.11-S1 were not assessed.)

Severity: High

Exploitable: Remotely

Description:

If a named caching resolver is configured with serve-stale-enable
yes, and with stale-answer-client-timeout set to 0 (the only
allowable value other than disabled), and if the resolver, in the
process of resolving a query, encounters a CNAME chain involving
a specific combination of cached or authoritative records, the
daemon will abort with an assertion failure.


Impact:

If an attacker is able to make queries that yield the necessary
combination of circumstances, they can force named to exit.

    Authoritative services are believed to be unaffected by this
vulnerability but it is important to read:
https://kb.isc.org/docs/why-does-my-authoritative-server-make-recursive-queries

    Resolvers are affected by this vulnerability.

CVSS Score: 7.5

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

For more information on the Common Vulnerability Scoring System and
to obtain your specific environmental score please visit:
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:H&version=3.1.


Workarounds:

Setting either of stale-answer-client-timeout off; or stale-answer-enable no;
in the configuration file will prevent the assertion.


Active exploits:

This flaw was discovered in internal testing. We are not aware of
any active exploits.


Solution:

Upgrade to the patched release most closely related to your current 
ersion of BIND:

    BIND 9.20.11
    BIND 9.21.10

BIND Supported Preview Edition is a special feature preview branch
of BIND provided to eligible ISC support customers.

    BIND 9.20.11-S1


Document revision history:

    1.0 Early Notification, 9 July 2025
    2.0 Public disclosure, 16 July 2025


Related documents:

See our BIND 9 Security Vulnerability Matrix for a complete listing
of security vulnerabilities and versions affected.

Do you still have questions? Questions regarding this advisory should
be mailed to bind-security@isc.org or posted as confidential GitLab
issues at
https://gitlab.isc.org/isc-projects/bind9/-/issues/new?issue[confidential]=true.

Note:

ISC patches only currently supported versions. When possible we
indicate EOL versions affected. (For current information on which
versions are actively supported, please see
https://www.isc.org/download/.)

ISC Security Vulnerability Disclosure Policy:

Details of our current security advisory policy and practice can
be found in the ISC Software Defect and Security Vulnerability
Disclosure Policy at https://kb.isc.org/docs/aa-00861.

The Knowledgebase article https://kb.isc.org/docs/cve-2025-40777
is the complete and official security advisory document.


Legal Disclaimer:

Internet Systems Consortium (ISC) is providing this notice on an
“AS IS” basis. No warranty or guarantee of any kind is expressed in
this notice and none should be implied. ISC expressly excludes and
disclaims any warranties regarding this notice or materials referred
to in this notice, including, without limitation, any implied
warranty of merchantability, fitness for a particular purpose,
absence of hidden defects, or of non-infringement. Your use or
reliance on this notice or materials referred to in this notice is
at your own risk. ISC may change this notice at any time. A
stand-alone copy or paraphrase of the text of this document that
omits the document URL is an uncontrolled copy. Uncontrolled copies
may lack important information, be out of date, or contain factual
errors.

____________________________________________________________________

New

    Published on Jul 16, 2025 

    Darren Ankney


CVE-2025-40776: Birthday Attack against Resolvers supporting ECS

CVE: CVE-2025-40776

Title: Birthday Attack against Resolvers supporting ECS

Document version: 2.0

Posting date: 16 July 2025

Program impacted: BIND 9

Versions affected:

BIND Supported Preview Edition

    9.11.3-S1 -> 9.16.50-S1
    9.18.11-S1 -> 9.18.37-S1
    9.20.9-S1 -> 9.20.10-S1

Versions NOT affected:

BIND

    9.0.0 -> 9.20.10

EDNS Client Subnet (ECS) options are only available in the BIND
Subscription Edition (-S), so only the -S edition is affected
by this CVE. End-of-Life (EOL) versions of BIND -S software are
believed to be affected, but were not tested.

Severity: High

Exploitable: Remotely

Description:

A named caching resolver that is configured to send ECS
(EDNS Client Subnet) options may be vulnerable to a
cache-poisoning attack.


Impact:

A resolver configured to send ECS options to authoritative servers
can be compelled to make queries that slightly increase the odds of
guessing the source port and other details necessary to bypass the
original birthday cache poisoning attack mitigations. As a result
of this weakness, a resolver with ECS enabled is more vulnerable to
successful cache poisoning via spoofed query responses than one that
does not implement this feature.

    Authoritative services are believed to be unaffected by this
vulnerability but it is important to read:
https://kb.isc.org/docs/why-does-my-authoritative-server-make-recursive-queries

    Resolvers are affected by this vulnerability.

CVSS Score: 8.6

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

For more information on the Common Vulnerability Scoring System and
to obtain your specific environmental score please visit:
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N&version=3.1.


Workarounds:

Disable ECS in BIND by removing the ecs-zones option from named.conf.

Active exploits:

We are not aware of any active exploits.


Solution:

Upgrade to the patched release most closely related to your current
version of BIND 9:

BIND Supported Preview Edition is a special feature preview branch
of BIND provided to eligible ISC support customers.

    9.18.38-S1
    9.20.11-S1


Acknowledgments:

ISC would like to thank Xiang Li from AOSP Lab of Nankai University
for bringing this vulnerability to our attention.


Document revision history:

    1.0 Early Notification, 9 July 2025
    2.0 Public disclosure, 16 July 2025


Related documents:

See our BIND 9 Security Vulnerability Matrix for a complete listing
of security vulnerabilities and versions affected.

Do you still have questions? Questions regarding this advisory
should be mailed to bind-security@isc.org or posted as confidential
GitLab issues at
https://gitlab.isc.org/isc-projects/bind9/-/issues/new?issue[confidential]=true.

Note:

ISC patches only currently supported versions. When possible we
indicate EOL versions affected. For current information on which
versions are actively supported, please see
https://www.isc.org/download/.

ISC Security Vulnerability Disclosure Policy:

Details of our current security advisory policy and practice can be
found in the ISC Software Defect and Security Vulnerability
Disclosure Policy at https://kb.isc.org/docs/aa-00861.

The Knowledgebase article https://kb.isc.org/docs/cve-2025-40776
is the complete and official security advisory document.


Legal Disclaimer:

Internet Systems Consortium (ISC) is providing this notice on an
"AS IS" basis. No warranty or guarantee of any kind is expressed
in this notice and none should be implied. ISC expressly excludes
and disclaims any warranties regarding this notice or materials
referred to in this notice, including, without limitation, any
implied warranty of merchantability, fitness for a particular
purpose, absence of hidden defects, or of non-infringement. Your
use or reliance on this notice or materials referred to in this
notice is at your own risk. ISC may change this notice at any time.
A stand-alone copy or paraphrase of the text of this document that
omits the document URL is an uncontrolled copy. Uncontrolled copies
may lack important information, be out of date, or contain factual
errors.


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