CVE-2025-40777

High

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. This issue affects BIND 9 versions 9.20.0 through 9.20.10, 9.21.0 through 9.21.9, and 9.20.9-S1 through 9.20.10-S1.

SeverityHigh

CVSS7.5

Exploit probability—

ProductBIND 9

PublishedJul 16, 2025

First seenJul 16, 2025

Weakness typeCWE-617CWE-617

How to fix

Vendor advisories

kb.isc.org/docs/cve-2025-40777

Affected products

Product	Affected versions	Fixed in
ISC BIND 9	9.20.0 ≤ v ≤ 9.20.10, 9.21.0 ≤ v ≤ 9.21.9, 9.20.9-S1 ≤ v ≤ 9.20.10-S1	—

Check your version

Choose the product and enter the version you run to see whether it falls in the affected range.

In the Intelligence 360 plan

Attack Surface Management

See the assets tied to your domains, the technologies they run and known vulnerabilities in one list.