CVE-2025-40775: DNS message with invalid TSIG causes an assertion failure

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 15.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-05-21 · updated 2026-06-17
Weakness: CWE-232

Description

When an incoming DNS protocol message includes a Transaction Signature (TSIG), BIND always checks it. If the TSIG contains an invalid value in the algorithm field, BIND immediately aborts with an assertion failure. This issue affects BIND 9 versions 9.20.0 through 9.20.8 and 9.21.0 through 9.21.7.

Affected products

ISC BIND: from 9.20.0 through 9.20.8; from 9.21.0 through 9.21.7

References

https://kb.isc.org/docs/cve-2025-40775
http://www.openwall.com/lists/oss-security/2025/05/21/1
https://security.netapp.com/advisory/ntap-20250523-0001/

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