CVE-2025-40775Network attack vector

Remote service crash via invalid TSIG algorithm

Published May 21, 2025 · Updated May 23, 2025

TSIG validation in ISC BIND 9 9.20.0 through 9.20.8 and 9.21.0 through 9.21.7 allows remote attackers to crash named. The DNS message parser accepts an invalid TSIG algorithm value and reaches an assertion during mandatory signature checking. A crafted DNS message can terminate either an authoritative server or resolver without authentication, interrupting DNS service.

CVSS severity7.5
High
EPSS probability15.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

TSIG validation in ISC BIND 9 9.20.0 through 9.20.8 and 9.21.0 through 9.21.7 allows remote attackers to crash named. The DNS message parser accepts an invalid TSIG algorithm value and reaches an assertion during mandatory signature checking. A crafted DNS message can terminate either an authoritative server or resolver without authentication, interrupting DNS service.

The record

CVE
CVE-2025-40775
Published
May 21, 2025
Updated
May 23, 2025
Vendor
Internet Systems Consortium
Product
BIND 9
Classifications
T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 21, 2025CVE publishedPublication date reported by the CVE source.
  2. May 23, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=9.20.0 <=9.20.8
  2. Affected versionversion=9.21.0 <=9.21.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Internet Systems Consortium · BIND 9version=9.20.0 <=9.20.8; version=9.21.0 <=9.21.7

Published CVSS scores

7.5Internet Systems ConsortiumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo